[Show abstract][Hide abstract] ABSTRACT: A unique platform for investigating the correlation between the
antiferromagnetic (AFM) and superconducting (SC) states in high temperature
superconductors is created by the discovery of alkaline iron selenide
superconductors which are composed of an AFM insulating phase and a SC phase
separated spatially. Our previous studies showed that pressure can fully
suppress the superconductivity of ambient-pressure superconducting phase (SC-I)
and AFM order simultaneously, then induce another superconducting phase (SC-II)
at higher pressure. Consequently, the connection between the two
superconducting phases becomes an intriguing issue. In this study, on the basis
of observing pressure-induced reemergence of superconductivity in
Rb0.8Fe2-ySe2-xTex (x=0, 0.19 and 0.28) superconductors, we find that the
superconductivity of the SC-I and SC-II phases as well as the AFM ordered state
can be synchronously tuned by Te doping and disappear together at the doping
level of x=0.4. We propose that the two superconducting phases are connected by
the AFM phase, in other words, the state of long-ranged AFM order plays a role
in giving rise to superconductivity of the SC-I phase, while the fluctuation
state of the suppressed AFM phase drives the emergence of SC-II phase. These
results comprehensively demonstrate the versatile roles of AFM states in
stabilizing and developing superconductivity in the alkaline iron selenide
[Show abstract][Hide abstract] ABSTRACT: Here, we report that K-doped BaMn2Bi2 shows no experimental evidence of
superconductivity down to 1.5 K under pressures up to 35.6 GPa, however, a
tetragonal to an orthorhombic phase transition is observed at pressure of 20
GPa. Theoretical calculations for the tetragonal and orthorhombic phases, on
basis of our high-pressure XRD data, find that the AFM order is robust in both
of the phases in pressurized Ba0.61K0.39Mn2Bi2. Our experimental and
theoretical results suggest that the K-doped BaMn2Bi2 belongs to a strong Hunds
AFM metal with a hybridization of localized spin electrons and itinerant
electrons, and that its robust AFM order essentially prevents the emergence of
[Show abstract][Hide abstract] ABSTRACT: Here, we report that K-doped BaMn2Bi2 shows no experimental evidence of superconductivity down to 1.5 K under pressures up to 35.6 GPa, however, a tetragonal to an orthorhombic phase transition is observed at pressure of 20 GPa. Theoretical calculations for the tetragonal and orthorhombic phases, on basis of our high-pressure XRD data, find that the AFM order is robust in both of the phases in pressurized Ba0.61K0.39Mn2Bi2. Our experimental and theoretical results suggest that the K-doped BaMn2Bi2 belongs to a strong Hunds AFM metal with a hybridization of localized spin electrons and itinerant electrons, and that its robust AFM order essentially prevents the emergence of superconductivity.
[Show abstract][Hide abstract] ABSTRACT: There is considerable interest in uncovering the physics of iron-based superconductivity from the alkaline iron selenides, a materials class containing an insulating phase (245 phase) and a superconducting (SC) phase. Due to the microstructural complexity of these superconductors, the role of the 245 phase in the development of the superconductivity has been a puzzle. Here we demonstrate a comprehensive high-pressure study on the insulating samples with pure 245 phase and biphasic SC samples. We find that the insulating behavior can be completely suppressed by pressure in the insulating samples and also identify an intermediate metallic (M') state. The Mott insulating (MI) state of the 245 phase and the M' state coexist over a significant range of pressure up to ̃10 GPa, the same pressure at which the superconductivity of the SC samples vanishes. Our results reveal the M' state as a pathway that connects the insulating and SC phases of the alkaline iron selenides and indicate that the coexistence and interplay between the MI and M' states is a necessary condition for superconductivity. Finally, we interpret the M' state in terms of an orbital selectivity of the correlated 3d electrons.
[Show abstract][Hide abstract] ABSTRACT: Pressure-induced superconductivity is oberserved in Ca10 (Pt3 As8 )(Fe2 As2 )5 by in situ high-pressure resistance and magnetic susceptibility measurements. Scaling of the pressure-induced and doping-induced superconductivity shows that the electronic phase diagrams of the pressurized and chemically doped 10-3-8 compound are similar in the moderate pressure and doping range but are disparate at higher pressure and heavy doping.
[Show abstract][Hide abstract] ABSTRACT: The emergence of superconductivity in the iron pnictide or cuprate high temperature superconductors usually accompanies the suppression of a long-ranged antiferromagnetic (AFM) order state in a corresponding parent compound by doping or pressurizing. A great deal of effort by doping has been made to find superconductivity in Mn-based compounds, which are thought to bridge the gap between the two families of high temperature superconductors, but the AFM order was not successfully suppressed. Here we report the first observations of the pressure-induced elimination of long-ranged AFM order at ~ 34 GPa and a crossover from an AFM insulating to an AFM metallic state at ~ 20 GPa in LaMnPO single crystals that are iso-structural to the LaFeAsO superconductor by in-situ high pressure resistance and ac susceptibility measurements. These findings are of importance to explore potential superconductivity in Mn-based compounds and to shed new light on the underlying mechanism of high temperature superconductivity.
[Show abstract][Hide abstract] ABSTRACT: The Ca10(PtnAs8)(Fe2As2)5 (n=3,4) compounds are a new type of iron pnictide
superconductor whose structures consist of stacking Ca-PtnAs8-Ca-Fe2As2 layers
in a unit cell. When n=3 (the 10-3-8 phase), the undoped compound is an
antiferromagnetic (AFM) semiconductor, while, when n=4 (the 10-4-8 phase), the
undoped compound is a superconductor (Tc=26K), a difference that has been
attributed to the electronic character of the PtnAs8 intermediary layers. Here
we report high-pressure studies on 10-3-8 and 10-4-8, using a combination of
in-situ resistance, magnetic susceptibility, Hall coefficient and X-ray
diffraction measurements. We find that the AFM order in undoped 10-3-8 is
suppressed completely at 3.5 GPa and that superconductivity then appears in the
3.5-7 GPa pressure range with a classic dome-like behavior. In contrast, Tc in
the 10-4-8 phase displays a monotonic decrease with increasing pressure. Our
results allow for the establishment of a unique correspondence between
pressure-induced and doping-induced superconductivity in the high-Tc iron
pnictides, and also points the way to an effective strategy for finding new
[Show abstract][Hide abstract] ABSTRACT: Here we show that a pressure of about 8 GPa suppresses both the vacancy order
and the insulating phase, and a further increase of the pressure to about 18
GPa induces a second transition or crossover. No superconductivity has been
found in compressed insulating 245 phase. The metallic phase in the
intermediate pressure range has a distinct behavior in the transport property,
which is also observed in the superconducting sample. We interpret this
intermediate metal as an orbital selective Mott phase (OSMP). Our results
suggest that the OSMP provides the physical pathway connecting the insulating
and superconducting phases of these iron selenide materials.
[Show abstract][Hide abstract] ABSTRACT: We highlight a few points on iron-based superconductors in this paper. Experimental evidence for intrinsic inhomogeneity and phase separation in Fe-based superconductors is reviewed first. The non-BCS feature and other similarities between the Fe-based superconductors and the cuprates are also presented. The pressure effect on the FeSe-based superconductors observed recently is then discussed in terms of the interplay between superconducting transition temperature and structural characters. It is suggested that there is room for exploring new superconductors with higher transition temperature and that the improvement on the sample quality is necessary for further investigation on the superconducting mechanism.
Solid State Communications 04/2012; 152(8):660–665. · 1.53 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Pressure has an essential role in the production and control of superconductivity in iron-based superconductors. Substitution of a large cation by a smaller rare-earth ion to simulate the pressure effect has raised the superconducting transition temperature T(c) to a record high of 55 K in these materials. In the same way as T(c) exhibits a bell-shaped curve of dependence on chemical doping, pressure-tuned T(c) typically drops monotonically after passing the optimal pressure. Here we report that in the superconducting iron chalcogenides, a second superconducting phase suddenly re-emerges above 11.5 GPa, after the T(c) drops from the first maximum of 32 K at 1 GPa. The T(c) of the re-emerging superconducting phase is considerably higher than the first maximum, reaching 48.0-48.7 K for Tl(0.6)Rb(0.4)Fe(1.67)Se(2), K(0.8)Fe(1.7)Se(2) and K(0.8)Fe(1.78)Se(2).
[Show abstract][Hide abstract] ABSTRACT: In this talk, we present our recent progress in effect of pressure on
superconductivity of newly discovered iron chalcogenide superconductors.
We show that the either positive or negative pressure can tune
superconductivity of this new kind of superconductors. Superconductivity
with higher superconducting transition temperature Tc can reemerge after
elimination of the initial superconducting phase upon compression. We
find that the maximum Tc of the reemerging superconducting phase is as
high as 48.7 K for K0.8Fe1.70Se2 and 48
K for Tl0.6Rb0.4Fe1.67Se2,
setting a new Tc record for chalcogenide superconductors. The presence
of the second superconducting phase is proposed to be related to
pressure-induced quantum criticality. Our findings open up the potential
route for the exploration of high-Tc superconductivity in iron-based and
[Show abstract][Hide abstract] ABSTRACT: Pressure plays an essential role in the induction1 and control2,3 of
superconductivity in iron-based superconductors. Substitution of a smaller
rare-earth ion for the bigger one to simulate the pressure effects has
surprisingly raised the superconducting transition temperature Tc to the record
high 55 K in these materials4,5. However, Tc always goes down after passing
through a maximum at some pressure and the superconductivity eventually tends
to disappear at sufficiently high pressures1-3. Here we show that the
superconductivity can reemerge with a much higher Tc after its destruction upon
compression from the ambient-condition value of around 31 K in newly discovered
iron chalcogenide superconductors. We find that in the second superconducting
phase the maximum Tc is as high as 48.7 K for K0.8Fe1.70Se2 and 48 K for
(Tl0.6Rb0.4)Fe1.67Se2, setting the new Tc record in chalcogenide
superconductors. The presence of the second superconducting phase is proposed
to be related to pressure-induced quantum criticality. Our findings point to
the potential route to the further achievement of high-Tc superconductivity in
iron-based and other superconductors.
[Show abstract][Hide abstract] ABSTRACT: We report the first experimental evidence for the intimate connection between
superconductivity and antiferromagnetism in Rb0.8Fe2Se2-xTex single crystal
under negative chemical pressure by substituting Se with isovalent Te atoms.
Electrical resistance measurements in the temperature range from 4 K to 550 K
demonstrate that both superconducting transition temperature (Tc) and Neel
temperature (TN) were suppressed continuously with the lattice expansion. When
the Te concentration x in Rb0.8Fe2Se2-xTex approaches 0.3, the superconducting
transition temperature Tc is completely suppressed and the sample behaves like
a semiconductor, meanwhile the characteristic peak of antiferromagnetic
transition on resistance curve disappears. Our observation suggests that the
pressure-induced lattice expansion can be used to tune the correlativity of
superconductivity and antiferromagnetism.
[Show abstract][Hide abstract] ABSTRACT: Pressure-induced superconductivity and its relation to the corresponding Hall coefficient (RH) have been investigated for Bi2Te3, a known topological insulator, through in situ measurements of magnetoresistance and ac susceptibility with diamond anvil cells. A full phase diagram is presented which shows a complex dependence of the superconducting transition temperature as a function of pressure over an extensive range. High-pressure RH measurements reveal a close relation to these complex behaviors; in particular, an abrupt change of dRH/dP is observed in crossing from the nonsuperconducting to the superconducting ambient-pressure phase.
[Show abstract][Hide abstract] ABSTRACT: The discovery of superconductivity of about 30 K in iron selenides with very
large magnetic moments simulates the examination of completing orders. Here we
report a finding of pressure- induced suppression of the superconducting
transition temperature Tc and enhancement of the temperature of the resistance
hump TH through charge transfer between two iron sites with different
occupancies. The activation energy for the electric transport of the
high-temperature resistance is observed to go to zero at a critical pressure of
8.7 GPa, at which superconductivity tends to disappear and the
semiconductor-to-metal transition takes place. Beyond the critical point, the
resistance exhibits a metallic behavior over the whole temperature range
studied. All these features indicate the existence of quantum criticality in
[Show abstract][Hide abstract] ABSTRACT: Superconductivity can be realized in Eu-containing pnictides by applying chemical (internal) and physical (external) pressure, the intrinsic physical mechanism of which attracts much attention in the studies of pnictide superconductors. Here we present the experimental evidence for the pressure-induced valence change of europium in EuFe2As1.4P0.6 exposed to ambient pressure and EuFe2As2 to high pressure by x-ray absorption measurements on L3-Eu edge. We found that the absorption spectrum of EuFe2As1.4P0.6 showed a clear spectra weight transfer from divalent to trivalent state. Furthermore, a similar behavior of valence transition as in EuFe2As1.4P0.6 was also observed in EuFe2As2 when pressure was applied. This reports the observation of valence change in pnictide superconductors and the analysis of its influence on superconductivity in EuFe2As1.4P0.6 and compressed EuFe2As2.
[Show abstract][Hide abstract] ABSTRACT: We studied high-pressure behavior of CeFeAsO1−xFx superconductors with x=0.16 and x=0.3 by in situ measurements of electrical resistance, X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS) with diamond anvil cell (DAC). A pressure-induced quantum phase transition from the superconducting state to the non-superconducting Kondo screened phase associated with a volume collapse was discovered in the layered CeFeAsO1−xFx compounds. The XAS data of Ce-L3 in CeFeAsO0.7F0.3 clearly show a spectral weight transfer from the main line to the satellite line after the transition, demonstrating that Ce's valence changes under high pressure. Comprehensive experimental results and analysis in this paper provide some insight into the connection among superconductivity, valence change and structural phase transition, which reveals a picture of pressure-induced competition between Kondo singlet and BCS singlet in the Ce-pnictide superconductors.
[Show abstract][Hide abstract] ABSTRACT: Pressure-induced superconductivity and its relation to corresponding Hall
coefficient (RH) have been reported for Bi2Te3, one of known topological
insulators. A full phase diagram is presented which shows a complex dependence
of the superconducting transition temperature as a function of pressure over an
extensive range. High-pressure RH measurements reveal a close relation of these
complex behaviors, particularly, a dramatic change of dRH/dP before structural
phase transition and a pressure-induced crossover on RH in the high pressure
phase were observed.
[Show abstract][Hide abstract] ABSTRACT: Here we report comprehensive studies of pressure effect on superconducting transition temperature (Tc) in optimally doped EuFe2As1.4P0.6 single crystal. We found that the Tc of the sample compressed at ~9 GPa was enhanced up to 48.3K, which is far beyond the ultimate temperature (39K) of MacMillan's prediction and sets the highest record in MFe2As2 system (M=Ca, Sr, Ba and Eu) so far. Obviously different from the pressure dependence of Tc in optimally doped BaFe2As1.3P0.7, the experimental results demonstrated that the pressure dependence of Tc for the sample investigated exhibited nonmonotonic behavior, i.e. the Tc increased with pressure initially before reaching the maximum at ~9 GPa, then dramatically decreased with further increasing pressure and disappeared at ~21 GPa eventually. In-situ x-ray diffraction (XRD) and x-ray absorption measurements with diamond anvil cells revealed that the pressure-induced valence transition of Eu ions was a favorable factor for the Tc enhancement, while the formation of collapsed tetragonal phase was a negative factor for the superconducting transition.
[Show abstract][Hide abstract] ABSTRACT: Superconductivity can be realized in Eu-containing pnictides by application of chemical (internal) and physical (external) pressure, the intrinsic physical mechanism of which attracts much attention in physics community. Here we present the experimental evidence for the valence change of europium in compounds of EuFe2As1.4P0.6 exposed to ambient pressure and EuFe2As2 to high pressure by x-ray absorption measurements on L3-Eu edge. We find that the absorption spectrum of EuFe2As1.4P0.6 at ambient pressure shows clear spectra weight transfer from a divalent to a trivalent state. Furthermore, application of pressure on EuFe2As2 using a diamond anvil cell shows a similar behavior of valence transition as EuFe2As1.4P0.6. These findings are the first observation of superconductivity mechanized by valence change in pnictides superconductors and elucidate the intrinsic physical origin of superconductivity in EuFe2As1.4P0.6 and compressed EuFe2As2. Comment: 13 pages, 3 fifures