Publications (291)570.4 Total impact
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ABSTRACT: We present a study of the crystal structure and physical properties of single crystals of a new Febased ternary compound, Zr2−xFe4Si16−y(x = 0.81, y = 6.06). Zr1.19Fe4Si9.94 is a layered compound, where stoichiometric βFeSi2derived slabs are separated by ZrSi planes with substantial numbers of vacancies. High resolution transmission electron microscopy (HRTEM) experiments show that these ZrSi layers consist of 3.5 nm domains where the Zr and Si vacancies are ordered within a supercell sixteen times the volume of the stoichiometric cell. Within these domains, the occupancies of the Zr and Si sites obey symmetry rules that permit only certain compositions, none of which by themselves reproduce the average composition found in xray diffraction experiments. Magnetic susceptibility and magnetization measurements reveal a small but appreciable number of magnetic moments that remain freely fluctuating to 1.8 K, while neutron diffraction confirms the absence of bulk magnetic order with a moment of 0.2μB or larger down to 1.5 K. Electrical resistivity measurements find that Zr1.19Fe4Si9.94 is metallic, and the modest value of the Sommerfeld coefficient of the specific heat γ = C/T suggests that quasiparticle masses are not particularly strongly enhanced. The onset of superconductivity at Tc 6 K results in a partial resistive transition and a small Meissner signal, although a bulklike transition is found in the specific heat. Sharp peaks in the ac susceptibility signal the interplay of the normal skin depth and the London penetration depth, typical of a system in which nanosized superconducting grains are separated by a nonsuperconducting host. Ultra low field differential magnetic susceptibility measurements reveal the presence of a surprisingly large number of trace magnetic and superconducting phases, suggesting that the ZrFeSi ternary system could be a potentially rich source of new bulk superconductors.Journal of Physics Condensed Matter 08/2014; 26(37):376002. · 2.22 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We investigated the occurrence and nature of superconductivity in single crystals of YFe$_2$Ge$_2$ grown out of Sn flux by employing xray diffraction, electrical resistivity, and specific heat measurements. We found that the residual resistivity ratio (RRR) of single crystals can be greatly improved, reaching as high as $\sim$60, by decanting the crystals from the molten Sn at $\sim$350$^\circ$C and/or by annealing at temperatures between 550$^\circ$C and 600$^\circ$C. We found that samples with RRR $\gtrsim$ 34 showed resistive signatures of superconductivity with the onset of the superconducting transition $T_c\approx1.4$ K. RRR values vary between 35 and 65 with, on average, no systematic change in $T_c$ value, indicating that systematic changes in RRR do not lead to comparable changes in $T_c$. Specific heat measurements on samples that showed clear resistive signatures of a superconducting transition did not show any signature of a superconducting phase transition, which suggests that the superconductivity observed in this compound is either some sort of filamentary, strain stabilized superconductivity associated with small amounts of stressed YFe$_2$Ge$_2$ (perhaps at twin boundaries or dislocations) or is a second crystallographic phase present at levels below detection capability of conventional powder xray techniques.08/2014;  [Show abstract] [Hide abstract]
ABSTRACT: Irradiation with 2.5 MeV electrons at doses up to 5.2 $\times$10$^{19}$ electrons/cm$^2$ was used to introduce pointlike defects in single crystals of Ba$_{1x}$K$_x$Fe$_2$As$_2$ with $x=$ 0.19 ($T_c=$ 14 K), $x=$ 0.26 ($T_c=$ 32 K) and 0.34 ($T_c=$ 39 K) to study the superconducting gap structure by probing the effect of nonmagnetic scattering on electrical resistivity, $\rho(T)$, and London penetration depth, $ \lambda (T)$. For all compositions, the irradiation suppressed the superconducting transition temperature, $T_c$ and increased resistivity. The low  temperature behavior of $\lambda (T)$ is best described by the power  law function, $\Delta \lambda (T) = A(T/T_c)^n$. While substantial suppression of $T_c$ supports $s_{\pm}$ pairing mechanism, in samples close to the optimal doping, $x=$ 0.26 and 0.34, the exponent $n$ remained high ($n \geq 3$) indicating robust full superconducting gaps. For the $x=$ 0.19 composition, exhibiting coexistence of superconductivity and long  range magnetism, the suppression of $T_c$ was much more rapid and the exponent $n$ decreased toward dirty limit of $n$ = 2. In this sample, the irradiation also suppressed the temperature of structural/magnetic transition, $T_{sm}$, from 103 K to 98 K consistent with the itinerant nature of the magnetic order. Our results suggest that underdoped compositions, especially in the coexisting regime are most susceptible to nonmagnetic scattering and imply that in multiband Ba$_{1x}$K$_x$Fe$_2$As$_2$ superconductors, the ratio of the interband to intraband pairing strength, and associated gap anisotropy, increases upon the departure from the optimal doping.07/2014;  [Show abstract] [Hide abstract]
ABSTRACT: Measurements of physical properties show that Yb enters the single crystals systematically and in registry with the nominal Yb concentration x of the starting material dissolved in the molten indium flux.07/2014;  [Show abstract] [Hide abstract]
ABSTRACT: The inplane London penetration depth, $\Delta\lambda(T)$, was measured using a tunnel diode resonator technique in single crystals of Ba$_{1x}$K$_{x}$Fe$_{2}$As$_{2}$ with doping levels $x$ ranging from heavily underdoped, $x$=0.16 ($T_{c}$=7~K) to nearly optimally doped, $x$= 0.34 ($T_{c}=$39 K). Exponential saturation of $\Delta\lambda(T)$ in the $T\to0$ limit is found in optimally doped samples, with the superfluid density $\rho_{s}(T)\equiv(\lambda(0)/\lambda(T))^{2}$ quantitatively described by a selfconsistent $\gamma$model with two nodeless isotropic superconducting gaps. As the doping level is decreased towards the extreme end of the superconducting dome at $x$=0.16, the lowtemperature behavior of $\Delta\lambda(T)$ becomes nonexponential and best described by the powerlaw $\Delta\lambda(T)\propto T^{2}$, characteristic of strongly anisotropic gaps. The change between the two regimes happens within the range of coexisting magnetic/nematic order and superconductivity, $x<0.25$, and is accompanied by a rapid rise in the absolute value of $\Delta\lambda(T)$ with underdoping. This effect, characteristic of the competition between superconductivity and other ordered states, is very similar to but of significantly smaller magnitude than what is observed in the electrondoped Ba(Fe$_{1x}$Co$_{x}$)$_{2}$As$_{2}$ compounds. Our study suggests that the competition between superconductivity and magnetic/nematic order in holedoped compounds is weaker than in electrondoped compounds, and that the anisotropy of the superconducting state in the underdoped iron pnictides is a consequence of the anisotropic changes in the pairing interaction and in the gap function promoted by both magnetic and nematic longrange order.06/2014;  [Show abstract] [Hide abstract]
ABSTRACT: London penetration depth, $\lambda (T)$, was measured in single crystals of K$_{1x}$Na$_x$Fe$_2$As$_2$, $x$=0 and 0.07, down to temperatures of 50~mK, $\sim T_c/50$. Isovalent substitution of Na for K significantly increases impurity scattering, with $\rho(T_c)$ rising from 0.2 to 2.2 $\mu \Omega$cm, and leads to a suppression of $T_c$ from 3.5~K to 2.8~K. At the same time, a close to $T$linear $\Delta \lambda (T)$ in pure samples changes to almost $T^2$ in the substituted samples. The behavior never becomes exponential as expected for the accidental nodes, as opposed to $T^2$ dependence in superconductors with symmetry imposed line nodes. The superfluid density in the full temperature range follows a simple clean and dirty $d$wave dependence, for pure and substituted samples, respectively. This result contradicts suggestions of multiband scenarios with strongly different gap structure on four sheets of the Fermi surface.06/2014;  [Show abstract] [Hide abstract]
ABSTRACT: London penetration depth, $\lambda(T)$, was measured in single crystals of SrFe$_2$(As$_{1x}$P$_x$)$_2$ ($x=$0.35) iron  based superconductor. The influence of disorder on the transition temperature, $T_c$, and on $\lambda(T)$ was investigated. The effects of scattering controlled by the annealing of asgrown crystals was compared with the effects of artificial disorder introduced by 2.5~MeV electron irradiation. The low temperature behavior of $\lambda(T)$ can be described by a powerlaw function, $\Delta \lambda (T)=AT^n$, with the exponent $n$ close to one in pristine annealed samples, as expected for superconducting gap with line nodes. Upon $1.2 \times 10^{19}$ \ecm irradiation, the exponent $n$ increases rapidly exceeding a dirty limit value of $n=$ 2 implying that the nodes in the superconducting gap are accidental and can be lifted by the disorder. The variation of the exponent $n$ with $T_c$ is much stronger in the irradiated crystals compared to the crystals in which disorder was controlled by the annealing of the growth defects. We discuss the results in terms of different influence of different types of disorder on intra and inter band scattering.06/2014;  [Show abstract] [Hide abstract]
ABSTRACT: The thermal conductivity kappa of the heavyfermion metal CeCoIn5 was measured in the normal and superconducting states as a function of temperature T and magnetic field H, for a current and field parallel to the [100] direction. Inside the superconducting state, when the field is lower than the upper critical field Hc2, kappa/T is found to increase as T approaches absolute zero, just as in a metal and in contrast to the behavior of all known superconductors. This is due to unpaired electrons on part of the Fermi surface, which dominate the transport above a certain field. The evolution of kappa/T with field reveals that the electronelectron scattering (or transport mass m^*) of those unpaired electrons diverges as H approaches Hc2 from below, in the same way that it does in the normal state as H approaches Hc2 from above. This shows that the unpaired electrons sense the proximity of the fieldtuned quantum critical point of CeCoIn5 at H^* = Hc2 even from inside the superconducting state. The fact that the quantum critical scattering of the unpaired electrons is much weaker than the average scattering of all electrons in the normal state reveals a kspace correlation between the strength of pairing and the strength of scattering, pointing to a common mechanism, presumably antiferromagnetic fluctuations.05/2014;  [Show abstract] [Hide abstract]
ABSTRACT: A single crystal of isovalently substituted Ba(Fe$_{1x}$Ru$_{x}$)$_2$As$_2$ ($x=0.24$) was sequentially irradiated with 2.5 MeV electrons up to a maximum dose of $2.1 \times 10^{19}$ electrons/cm^2. The electrical resistivity was measured \textit{in  situ} at $T=$22 K during the irradiation and \textit{ex  situ} as a function of temperature between subsequent irradiation runs. Upon irradiation, the superconducting transition temperature, $T_c$, decreases and the residual resistivity, $\rho_0$, increases. We find that electron irradiation leads to the fastest suppression of $T_c$ compared to other types of artificially introduced disorder, probably due to the strong shortrange potential of the pointlike irradiation defects. A more detailed analysis within a multiband scenario with variable scattering potential strength shows that the observed $T_c$ vs. $\rho_0$ is fully compatible with $s_\pm$ pairing, in contrast to earlier claims that this model leads to a too rapid a suppression of $T_c$ with scattering.05/2014;  [Show abstract] [Hide abstract]
ABSTRACT: A single crystal of isovalently substituted Ba(Fe$_{1x}$Ru$_{x}$)$_2$As$_2$ ($x=0.24$) was sequentially irradiated with 2.5 MeV electrons up to a maximum dose of $2.1 \times 10^{19}$ electrons/cm^2. The electrical resistivity was measured \textit{in  situ} at $T=$22 K during the irradiation and \textit{ex  situ} as a function of temperature between subsequent irradiation runs. Upon irradiation, the superconducting transition temperature, $T_c$, decreases and the residual resistivity, $\rho_0$, increases. We find that electron irradiation leads to the fastest suppression of $T_c$ compared to other types of artificially introduced disorder, probably due to the strong shortrange potential of the pointlike irradiation defects. A more detailed analysis within a multiband scenario with variable scattering potential strength shows that the observed $T_c$ vs. $\rho_0$ is fully compatible with $s_\pm$ pairing, in contrast to earlier claims that this model leads to a too rapid a suppression of $T_c$ with scattering.04/2014;  [Show abstract] [Hide abstract]
ABSTRACT: We investigate infrared manifestations of the pseudogap in the prototypical cuprate and pnictide superconductors: YBa2Cu3Oy and BaFe2As2 (Ba122) systems. We find remarkable similarities between the spectroscopic features attributable to the pseudogap in these two classes of superconductors. The hallmarks of the pseudogap state in both systems include a weak absorption feature at about 500 cm1 followed by a featureless continuum between 500 and 1500 cm1 in the conductivity data and a significant suppression in the scattering rate below 700  900 cm1. The latter result allows us to identify the energy scale associated with the pseudogap $\Delta_{PG}$. We find that in the Ba122based materials the superconductivityinduced changes of the infrared spectra occur in the frequency region below 100  200 cm1, which is much lower than the energy scale of the pseudogap. We performed theoretical analysis of the scattering rate data of the two compounds using the same model which accounts for the effects of the pseudogap and electronboson coupling. We find that the scattering rate suppression in Ba122based compounds below $\Delta_{PG}$ is solely due to the pseudogap formation whereas the impact of the electronboson coupling effects is limited to lower frequencies. The magnetic resonance modes used as inputs in our modeling are found to evolve with the development of the pseudogap, suggesting an intimate correlation between the pseudogap and magnetism.04/2014;  [Show abstract] [Hide abstract]
ABSTRACT: The London penetration depth, $\lambda (T)$ was measured in single crystals of Ce$_{1x}R_x$CoIn$_5$, $R$=La, Nd and Yb down to 50~mK ($T_c/T \sim$50) using a tunneldiode resonator. In the cleanest samples $\Delta \lambda (T)$ is best described by the power law, $\Delta \lambda (T) \propto T^{n}$, with $n \sim 1$, consistent with line nodes. Substitutions of Ce with La, Nd and Yb lead to similar monotonic suppressions of $T_c$, however the effects on $\Delta \lambda(T)$ differ. While La and Nd doping results in an increase of the exponent to $n \sim 2$, as expected for a dirty nodal superconductor, Yb doping leads to $n > 3$, inconsistent with nodes, suggesting a change from nodal to nodeless superconductivity where Fermi surface topology changes were reported, implying that the nodal structure and Fermi surface topology are closely linked.04/2014; 
Article: Interplane resistivity of underdoped single crystals (Ba$_{1x}$K$_x$)Fe$_2$As$_2$, $0 \leq x<0.34$
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ABSTRACT: Temperaturedependent interplane resistivity, $\rho _c(T)$, was measured in holedoped ironarsenide superconductor (Ba$_{1x}$K$_x$)Fe$_2$As$_2$ over a doping range from parent compound to optimal doping $T_c\approx 38~K$, $0\leq x \leq 0.34$. Measurements were undertaken on highquality single crystals grown from FeAs flux. The coupled magnetic/structural transition at $T_{SM}$ leads to clear accelerated decrease of $\rho_c(T)$ on cooling in samples with $T_c <$26~K ($x <0.25$). This decrease in holedoped material is in notable contrast to an increase in $\rho_c(T)$ in the electrondoped Ba(Fe$_{1x}$Co$_x$)Fe $_2$As$_2$ and isoelectron substituted BaFe$_2$(As$_{1x}$P$_x$)$_2$. The $T_{SM}$ decreases very sharply with doping, dropping from $T_s$=71~K to zero on increase of $T_c$ from approximately 25 to 27~K. The $\rho_c(T)$ becomes $T$linear close to optimal doping. The broad crossover maximum in $\rho_c(T)$, found in the parent BaFe$_2$As$_2$ at around $T_{max} \sim$200~K, shifts to higher temperature $\sim$250~K with doping $x$=0.34. The maximum shows clear correlation with the broad crossover feature found in the temperaturedependent inplane resistivity $\rho_a(T)$. The doping evolution of $T_{max}$ in (Ba$_{1x}$K$_x$)Fe$_2$As$_2$ is in notable contrast with both rapid suppression of $T_{max}$ found in Ba(Fe$_{1x}TM_x$)$_2$As$_2$ ($TM$=Co,Rh,Ni,Pd) and its rapid increase BaFe$_2$(As$_{1x}$P$_x$)$_2$. This observation suggest that pseudogap features are much stronger in holedoped than in electrondoped ironbased superconductors, revealing significant electronhole doping asymmetry similar to the cuprates. This paper replaces: condmat:1106.0533.04/2014;  [Show abstract] [Hide abstract]
ABSTRACT: We investigate infrared manifestations of the pseudogap in the prototypical cuprate and pnictide superconductors: YBa2Cu3Oy and BaFe2As2 (Ba122) systems. We find remarkable similarities between the spectroscopic features attributable to the pseudogap in these two classes of superconductors. The hallmarks of the pseudogap state in both systems include a weak absorption feature at about 500 cm1 followed by a featureless continuum between 500 and 1500 cm1 in the conductivity data and a significant suppression in the scattering rate below 700  900 cm1. The latter result allows us to identify the energy scale associated with the pseudogap $\Delta_{PG}$. We find that in the Ba122based materials the superconductivityinduced changes of the infrared spectra occur in the frequency region below 100  200 cm1, which is much lower than the energy scale of the pseudogap. We performed theoretical analysis of the scattering rate data of the two compounds using the same model which accounts for the effects of the pseudogap and electronboson coupling. We find that the scattering rate suppression in Ba122based compounds below $\Delta_{PG}$ is solely due to the pseudogap formation whereas the impact of the electronboson coupling effects is limited to lower frequencies. The magnetic resonance modes used as inputs in our modeling are found to evolve with the development of the pseudogap, suggesting an intimate correlation between the pseudogap and magnetism.03/2014;  [Show abstract] [Hide abstract]
ABSTRACT: We present the superconducting and normal state properties of CaPd2Ge2 single crystal investigated by magnetic susceptibility \chi, isothermal magnetization M, heat capacity C_p, inplane electrical resistivity \rho and London penetration depth \lambda versus temperature T and magnetic field H measurements. Bulk superconductivity is inferred from the \rho(T) and C_p(T) data. The \rho(T) data exhibit metallic behavior and undergoes a superconducting transition with T_c onset = 1.98 K and zero resistivity state at T_c 0 = 1.67 K. The \chi(T) reveal the onset of superconductivity at 2.0 K. For T>2.0 K, the \chi(T) and M(H) are weakly anisotropic paramagnetic with \chi_ab > \chi_c. The C_p(T) confirm the bulk superconductivity below T_c = 1.69(3) K. The superconducting state electronic heat capacity is analyzed within the framework of a singleband \alphamodel of BCS superconductivity and various normal and superconducting state parameters are estimated. Within the \alphamodel, the C_p(T) data and the ab plane \lambda(T) data consistently indicate a moderately anisotropic swave gap with \Delta(0)/k_B T_c ~ 1.6, somewhat smaller than the BCS value of 1.764. The relationship of the heat capacity jump at T_c and the penetration depth measurement to the anisotropy in the swave gap is discussed.Journal of Physics Condensed Matter 03/2014; 26(40). · 2.22 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: Large highquality single crystals of holedoped ironbased superconductor (Ba$_{1x}$K$_x$)Fe$_2$As$_2$ were grown over a broad composition range $0.22 \leq x \leq 1$ by inverted temperature gradient method. We found that high soaking temperature, fast cooling rate, and adjusted temperature window of the growth are necessary to obtain single crystals of heavily K doped crystals (0.65$\leq x \leq$ 0.92) with narrow compositional distributions as revealed by sharp superconducting transitions in magnetization measurements and close to 100% superconducting volume fraction. The crystals were extensively characterized by xray and compositional analysis, revealing monotonic evolution of the $c$axis crystal lattice parameter with K substitution. Quantitative measurements of the temperaturedependent inplane resistivity, $\rho(T)$ found dopingindependent, constant within error bars, resistivity at room temperature, $\rho(300K)$, in sharp contrast with significant doping dependence in electron and isovalent substituted BaFe$_2$As$_2$ based compositions. The shape of the temperature dependent resistivity, $\rho(T)$, shows systematic dopingevolution, being close to $T^2$ in overdoped and revealing significant contribution of the $T$linear component at optimum doping. The slope of the upper critical field, $d H_{c2}/dT$, scales linearly with $T_c$ for both $H\parallel c$, $ H_{c2,c}$, and $H \parallel ab$, $H_{c2,ab}$. The anisotropy of the upper critical field, $\gamma \equiv H_{c2,ab} / H_{c2,c}$ determined near zerofield $T_c$ increases from $\sim$2 to 45 with increasing K doping level from optimal $x \sim$0.4 to strongly overdoped $x$=1.03/2014; 89(13).  [Show abstract] [Hide abstract]
ABSTRACT: We report measurements of electrical resistivity under pressure up to 5.8 GPa, magnetization up to 6.7 GPa and ac susceptibility up to 7.1 GPa in KFe2As2. At a pressure pc= 1.8 GPa, there is a change of slope in the pressure dependence of the superconducting transition temperature Tc(p) as previously reported. Above pc, Tc is almost constant up to 7 GPa. The Tp phase diagram is very sensitive to the pressure conditions as a consequence of anisotropic uniaxial pressure dependence of Tc. In addition, we observe a change in the upper critical field behavior across pc and provide a quantitative measure of this change. We show how this can be used to investigate a change of the superconducting gap structure and suggest the appearance of a kz modulation of the superconducting gap as a possible explanation.02/2014;  [Show abstract] [Hide abstract]
ABSTRACT: The inplane thermal conductivity κ and electrical resistivity ρ of the heavyfermion metal YbRh2Si2 were measured down to 50 mK for magnetic fields H parallel and perpendicular to the tetragonal c axis, through the fieldtuned quantum critical point Hc, at which antiferromagnetic order ends. The thermal and electrical resistivities, w ≡L0T/κ and ρ, show a linear temperature dependence below 1 K, typical of the nonFermiliquid behavior found near antiferromagnetic quantum critical points, but this dependence does not persist down to T =0. Below a characteristic temperature T≃0.35 K, which depends weakly on H, w (T) and ρ (T) both deviate downward and converge as T →0. We propose that T marks the onset of shortrange magnetic correlations, persisting beyond Hc. By comparing samples of different purity, we conclude that the WiedemannFranz law holds in YbRh2Si2, even at Hc, implying that no fundamental breakdown of quasiparticle behavior occurs in this material. The overall phenomenology of heat and charge transport in YbRh2Si2 is similar to that observed in the heavyfermion metal CeCoIn5, near its own fieldtuned quantum critical point.12/2013; 89(4).  [Show abstract] [Hide abstract]
ABSTRACT: In the approximation of validity of the Drude expression for quasiparticle conductivity and the assumption that all electrons at T = 0 transform into a superfluide condensate, the expression for the quasiparticle scattering rate tau 1 in terms of the real and imaginary parts of the microwave surface impedance has been obtained. The resulting expression is a generalization of the wellknown expression for tau^1, valid for omega x tau is much less 1, to an arbitrary value of omega x tau, where omega is the frequency of the microwave field. From experimental Kaband impedance measurements, temperature dependence of tau^1 in superconducting single crystal pnictides Ba(Fe1xCox)2As2 is obtained using the generalized expression. It is shown that under condition of the given work, the approximation omega x tau is much less 1 gives the considerable error in determination of tau^1.10/2013; 39(12).  [Show abstract] [Hide abstract]
ABSTRACT: Irradiation with 1.4 GeV $^{208}$Pb ions was used to induce artificial disorder in single crystals of ironarsenide superconductor Ba(Fe$_{1x}$Co$_x$)$_2$As$_2$ and to study its effect on the temperaturedependent London penetration depth and transport properties. Study was undertaken on overdoped single crystals with $x$=0.108 and $x$=0.127 characterized by notable modulation of the superconducting gap. Irradiation with doses 2.22$\times10^{11}$$\textit{d}$/cm$^2$ and 2.4$\times10^{11}$$\textit{d}$/cm$^2$, corresponding to the matching fields of $B_{\phi} = $6 T and 6.5 T, respectively, suppresses the superconducting $T_c$ by approximately 0.3 to 1 K. The variation of the lowtemperature penetration depth in both pristine and irradiated samples is well described by the powerlaw, $\Delta \lambda (T)=AT^n$. Irradiation increases the magnitude of the prefactor $A$ and decreases the exponent $n$, similar to the effect of irradiation in optimally doped samples. This finding supports universal $s_{\pm}$ pairing in Ba(Fe$_{1x}$Co$_x$)$_2$As$_2$ compounds for the whole Co doping range.Physical Review B. 08/2013; 88(5).
Publication Stats
2k  Citations  
570.40  Total Impact Points  
Top Journals
Institutions

2008–2014

Iowa State University
 Department of Physics and Astronomy
Ames, Iowa, United States


2012–2013

Hanyang University
Sŏul, Seoul, South Korea


2010–2013

Canadian Institute For Advanced Research
Toronto, Ontario, Canada


2006–2012

Université de Sherbrooke
 Department of Physics
Sherbrooke, Quebec, Canada


2011

Sungkyunkwan University
 Department of Physics
Seoul, Seoul, South Korea


2004–2006

University of Toronto
 Department of Physics
Toronto, Ontario, Canada


1997–2005

Kyoto University
 Department of Physics II
Kyoto, Kyotofu, Japan


2003

Himeji Institute of Technology
Kioto, Kyōto, Japan


1998–1999

National Academy of Sciences of Ukraine
Kievo, Kyiv City, Ukraine
