Alexander Chudnovskiy

• Hamburg University

We address Coulomb drag and near-field heat transfer in a double-layer system of incoherent metals. Each layer is modeled by an array of tunnel-coupled SYK dots with random interlayer interactions. Depending on the strength of intradot interactions and interdot tunneling, this model captures the crossover from the Fermi liquid to a strange metal ph...

We address Coulomb drag and near-field heat transfer in a double-layer system of incoherent metals. Each layer is modeled by an array of tunnel-coupled SYK dots with random inter-layer interactions. Depending on the strength of intra-dot interactions and inter-dot tunneling, this model captures the crossover from the Fermi liquid to a strange metal...

We present a model of a strongly correlated system with a non-Fermi liquid high temperature phase. Its ground state undergoes an insulator to superconductor quantum phase transition (QPT) as a function of a pairing interaction strength. Both the insulator and the superconductor are originating from the same interaction mechanism. The resistivity in...

We present a model of a strongly correlated system with a non-Fermi liquid high temperature phase. Its ground state undergoes an insulator to superconductor quantum phase transition (QPT) as a function of a pairing interaction strength. Both the insulator and the superconductor are originating from the same interaction mechanism. The resistivity in...

The Sachdev-Ye-Kitaev (SYK) model has emerged as a new paradigm of non-Fermi-liquid behavior. Here we investigate a possibility of having a superconducting off-diagonal long-range order (ODLRO) and a pseudogap phase within the SYK framework. We found that ODLRO may be established in a spin-1/2 version of the model with the time-reversal invariance...

Sachdev-Ye-Kitaev (SYK) model has emerged as a new paradigm of the non-Fermi-liquid behavior. Here we investigate a possibility of having a superconducting off-diagonal long-range order (ODLRO) and a pseudogap phase within the SYK framework. We found that ODLRO may be established in spin-1/2 version of the model with the time-reversal invariance an...

A bstract We investigate existence of replica off-diagonal solutions in the field-theoretical description of Sachdev-Ye-Kitaev model. To this end we evaluate a set of local and non-local dynamic correlation functions in the long time limit. We argue that the structure of the soft-mode Schwarzian action is qualitatively different in replica-diagonal...

We investigate existence of replica off-diagonal solutions in the field-theoretical description of Sachdev-Ye-Kitaev model. To this end we evaluate a set of local and non-local dynamic correlation functions in the long time limit. We argue that the structure of the soft-mode Schwarzian action is qualitatively different in replica-diagonal vs. repli...

Bose Einstein condensates of spin-1 atoms are known to exist in two different phases, both having spontaneously broken spin-rotation symmetry, a ferromagnetic and a polar condensate. Here we show that in two spatial dimensions it is possible to achieve a quantum phase transition from a polar condensate into a singlet phase symmetric under rotations...

We study the stability of multiple conducting edge states in a topological insulator against all multiparticle perturbations allowed by time-reversal symmetry. We model a system as a multichannel Luttinger liquid, where the number of channels equals the number of Kramers doublets at the edge. We show that in a clean system with N Kramers doublets t...

We study stability of multiple conducting edge states in a topological insulator against all multi-particle perturbations allowed by the time-reversal symmetry. We model a system as a multi-channel Luttinger liquid, where the number of channels equals the number of Kramers doublets at the edge. We show that in the clean system with N Kramers double...

Spin-1 Bose gas with anti-ferromagnetic interactions can form a Bose condensate of singlet pairs (singlet molecules) at low concentrations of atoms. We show that despite the effective attractive inter-atomic interactions in spin-singlet channel, the molecular condensate can be stabilized against further collapse due to the repulsive interactions in...

We investigate the effect of both strong and weak potential scattering in the array of Luttinger liquid wires with an arbitrary finite range inter-wire interactions. We find that finite range interaction stabilises metallic phase unreachable otherwise. Based on calculation of the scaling dimensions of one-particle scattering operators, we construct...

We investigate the effect of both strong and weak potential scattering caused by local impurities and extended (line) defects in the array of Luttinger liquid wires. We find that in both cases a finite range inter-wire interaction stabilises metallic state. Based on calculation of the scaling dimensions of one-particle scattering operators, we cons...

We propose a protocol which utilises radio frequency magnetic pulses in order to tune the effective two-particle scattering amplitudes for alkali atoms in the $F=1$ hyperfine ground state. Unlike the Feshbach resonance method, the proposed protocol preserves with controllable accuracy the global rotational symmetry in the spin space offering access...

The ferromagnet-topological insulator-ferromagnet (FM-TI-FM) junction exhibits thermal and electrical quantum Hall effects. The generated Hall voltage and transverse temperature gradient can be controlled by the directions of magnetizations in the FM leads, which inspires the use of FM-TI-FM junctions as electrical and as heat switches in spintroni...

In this paper, we review the theory of spin switching for systems of different sizes, from a quantum mechanical master equation approach for small atomic clusters to the quasiclassical description of spin dynamics by a stochastic Landau–Lifshits–Gilbert equation in metallic nanoscale magnetic systems. We present characteristic results emphasizing t...

Ferromagnet-topological insulator-ferromagnet (FM-TI-FM) junction exhibits thermal and electrical quantum Hall effects. The generated Hall voltage and transverse temperature gradient can be controlled by the angle between the magnetizations of the ferromagnetic leads, which inspires the use of FM-TI-FM junctions as electrical and heat switches in s...

The ferromagnet-topological insulator-ferromagnet (FM-TI-FM) junction exhibits thermal and electrical quantum Hall effects. The generated Hall voltage and transverse temperature gradient can be controlled by the directions of magnetizations in the FM leads, which inspires the use of FM-TI-FM junctions as electrical and as heat switches in spintroni...

Scattering by magnetic impurities is known to destroy coherence of electron motion in metals and semiconductors. We investigate the decoherence introduced in a single act of electron scattering by a magnetic impurity in a quantum Hall system. To this end we introduce a fictitious nonunitary scattering matrix $\mathcal{S}$ for electrons that reprodu...

Decay of a high-energy double occupancy state, doublon, in a narrow-band lattice requires creation of a coherent many-particle excitation. This leads to an exponentially long relaxation time of such a state. We show that, if the average occupation number is sufficiently small, the corresponding exponent may be evaluated exactly. To this end we deve...

We present a generalization of the recently developed dual fermion approach introduced for correlated lattices to non-equilibrium problems. In its local limit, the approach has been used to devise an efficient impurity solver, the superperturbation solver for the Anderson impurity model (AIM). Here we show that the general dual perturbation theory...

We explore how non-equilibrium noise affects spin-torque switching elements and oscillators. To do so we first discuss the deterministic dynamics of magnetic tunnel junctions, introducing a convenient set of slow and fast degrees of freedom. We then derive effective Langevin equation for the slowly varying energy of precessional orbit and introduce...

We investigate the role of equilibrium and nonequilibrium noise in the magnetization dynamics on mono-domain ferromagnets. Starting from a microscopic model we present a detailed derivation of the spin shot noise correlator. We investigate the ramifications of the nonequilibrium noise on the spin torque dynamics, both in the steady state precession...

Manipulation of magnetization by electric current lies in the mainstream of the rapidly developing field of spintronics. The electric current influences the magnetization through the spin-torque effect. Entering a magnet, spin-polarized current exerts a torque on the magnetization, which aligns the magnetization parallel or antiparallel to the spin...

We formulate a generalized Chalker--Coddington network model that describes the effect of nuclear spins on the two-dimensional electron gas in the quantum Hall regime. We find exact analytical expression for the transmission coefficient of a charged particle through a saddle point potential in presence of perpendicular magnetic field that takes int...

Absorption of energy quanta generated by a quantum point contact results in the inelastic current through a double quantum dot placed nearby. In contrast to a single quantum dot, the inelastic current through the double quantum dot is determined by the nonlocal current correlations in the quantum point contact, which results in its sensitivity to t...

Clusters of magnetic atoms lying on a metallic substrate can exhibit Kondo effect due to the exchange interaction with mobile electrons in the metal, which can be observed in STM measurements. The same interaction results in the induced RKKY interaction between the magnetic moments in the cluster. For different geometries of the cluster, it can enh...

A spin polarized current may transfer angular momentum to a ferromagnet, resulting in a spin-torque phenomenon. At the same time the shot noise, associated with the current, leads to a nonequilibrium stochastic force acting on the ferromagnet. We derive a stochastic version of the Landau-Lifshitz-Gilbert equation for a magnetization of a "free" fer...

Spin polarized current may transfer angular momentum to a ferromagnet, resulting in a spin-torque phenomenon. At the same time the shot noise, associated with the current, leads to a non-equilibrium stochastic force acting on the ferromagnet. We derive stochastic version of Landau-Lifshitz-Gilbert equation for a magnetization of a ''free'' ferromag...

We calculate the tunneling density of states for a Tomonaga-Luttinger liquid placed under a strong bias voltage. For the tunneling through a side-coupled point contact, one can observe the power law singularities in the tunneling density of states separately for the right- and left-movers despite the point-like tunnel contact. The calculated nonequ...

We present a theoretical description of the current through a double quantum dot driven by charge fluctuations at a quantum point contact placed nearby. We find that at a particular plateau-like energy dependence of the transmission $t_{\epsilon}$ of the quantum point contact the current onset is determined not by the energy conservation condition...

We consider spin and orbital Kondo effect in a parallel arrangement of two strongly electrostatically coupled quantum dots. Increasing the exchange of electrons between the dots through the attached leads induces a smooth crossover between SU(4) spin- and orbital Kondo effect and SU(2) spin Kondo effect. Being the same for the SU(4) and SU(2) symme...

We calculate the tunneling density of states for a Tomonaga-Luttinger liquid placed under a strong bias voltage. For the tunneling through a side-coupled point contact, one can observe the power law singularities in the tunneling density of states separately for the right- and left-movers despite the point-like tunnel contact. Deviations of the non...

We study localization-delocalization transition in quantum Hall systems with a random field of nuclear spins acting on two-dimensional (2d) electron spins via hyperfine contact (Fermi) interaction. We use Chalker-Coddington network model, which corresponds to the projec-tion onto the lowest Landau level. The inhomogeneous nuclear polar-ization acts...

We analyze electron transport through the triple-quantum-dot system. The equations of motion for the electron Green's functions are derived and the expression for the electric current is obtained. We show that the current-voltage characteristics of this structure can exhibit negative differential conductance.

We have found a manifestation of spin-orbit Berry phase in the conductance of a mesoscopic loop with Rashba spin-orbit coupling placed in an external magnetic field perpendicular to the loop plane. In detail, the transmission probabilities for a straight quantum wire and for a quantum loop made of the same wire have been calculated and compared wit...

We consider the spin and orbital Kondo effect in a parallel arrangement of two strongly electrostatically coupled quantum dots. Increasing the exchange of electrons between the dots through the attached leads induces a transition between the SU(4) spin- and orbital Kondo effect and SU(2) spin Kondo effect. Being the same for the SU(4) and SU(2) sym...

Phononless plasmon assisted transport through a long disordered array of finite length quantum wires is investigated analytically. Generically strong electron plasmon interaction in quantum wires results in a qualitative change of the temperature dependence of thermally activated resistance in comparison to phonon assisted transport. At high temper...

We propose a semiconductor structure that can switch the electron spin using the interplay between the Rashba effect and the geometry of the system. In detail, the structure consists of a strongly curved one-dimensional ballistic wire with intrinsic spin-orbit interactions. Here, in contrast to the previous proposals based on straight quantum chann...

Phononless plasmon assisted transport through a long disordered array of finite length quantum wires is investigated analytically. Two temperature regimes, the low- and the high-temperature ones, with qualitatively different temperature dependencies of thermally activated resistance are identified. The characteristics of plasmon assisted and phonon...

We propose a semiconductor structure that can rotate the electron spin without using ferromagnetic contacts, tunneling barriers, external radiation etc. The structure consists of a strongly curved one-dimensional ballistic wire with intrinsic spin-orbit interactions of Rashba type. Our calculations and analytical formulae show that the proposed dev...

We consider the spin and orbital Kondo effect in a parallel arrangement of two strongly electrostatically coupled quantum dots. Increasing the exchange of electrons between the dots through the attached leads induces the transition between the SU(4) spin- and orbital Kondo effect and SU(2) spin Kondo effect. Being the same for the SU(4) and SU(2) s...

A double quantum dot is coupled in parallel for studying the competition between the pseudospin Kondo correlations and strongly hybridized molecular states. Cryogenic measurements are performed in the regime of weak coupling of the two dots to leads under linear transport conditions. A detailed theoretical model is presented which verifies the find...

The current–voltage (I–V) characteristics for perpendicular transport through two sequentially coupled wires of finite length is calculated analytically. Due to interwire interactions, the positions of steps in the I–V characteristics shift to lower voltages in comparison to noninteracting wires, which reflects the facilitation of current by intera...

The European Physical Society (EPS) is a not for profit association whose members include 41 National Physical Societies in Europe, individuals from all fields of physics, and European research institutions. As a learned society, the EPS engages in activities that strengthen ties among the physicists in Europe. As a federation of National Physical...

We consider a thermally activated transport across and array of parallel one-dimensional quantum wires of finite length (quantum stubs). The disorder enters as a random tunneling between the nearest-neighbor stubs as well as a random shift of the bottom of the energy band in each stub. Whereas one-particle wave functions are localized across the ar...

We investigate theoretically the linear conductance of a two-level quantum dot as a function of the gate voltage and different strength of coupling to the external electronic system (the reservoir). Apart from the weak coupling regime, characterized by the Kondo-enhancement of the conductance in the spinful ground state, a strong coupling regime, w...

We study the energy spectrum and the persistent current in an ideal one-dimensional mesoscopic ring coupled to a fermionic reservoir. We find that the tunnel coupling in general leads to the suppression of the persistent current. However, with increasing coupling, the effective level structure of the ring coupled to the reservoir changes and quasis...

We study the energy spectrum and the persistent current in an ideal one-dimensional mesoscopic ring coupled to an external fermionic reservoir. The contact between ring and reservoir is described by a tunneling operator, which causes an indirect coupling between different ring states via states in the reservoir. For strong coupling to the reservoir...

The European Physical Society (EPS) is a not for profit association whose members include 41 National Physical Societies in Europe, individuals from all fields of physics, and European research institutions. As a learned society, the EPS engages in activities that strengthen ties among the physicists in Europe. As a federation of National Physical...

We study the localization of a heteropolymer with Gaussian distributed random sequences onto an homogeneous surface, the problem which is equivalent to the wetting of an interface at a disordered substrate in two dimensions, via replica trick by using the Green's function technique. We present analytical results of the study of one- and two-replica...

Influence of disorder on the ferromagnetic phase transition in diluted (III,Mn)V semiconductors is investigated analytically. The regime of small disorder is addressed, and the enhancement of the critical temperature by disorder is found both in the mean field approximation and from the analysis of the zero temperature spin stiffness. Due to disord...

We study the localization of a random heteropolymer onto an homogeneous surface, the problem which is equivalent to the wetting of an interface at disordered substrate in two dimensions, via replica trick by using the Green's function technique. The exact treatment of one- and two-replica binding states is used to compute the free energy of the ran...

We investigate the dependence of the ground state of a multilevel quantum dot on the coupling to an external fermionic system and on the interactions in the dot. As the coupling to the external system increases, the rearrangement of the effective energy levels in the dot signals the transition from the Kondo regime to a mixed-valence (MV) regime. T...

A quantum dot (QD) immersed into either a clean or diffusive Fermi liquid is considered in different regimes, determined by the applied gate voltage. The Kondo regime for non-zero spin in the dot and the Fermi liquid regime for zero spin in the dot are identified. Using an effective field theory description, the charge and spin fluctuations in the...

The European Physical Society (EPS) is a not for profit association whose members include 41 National Physical Societies in Europe, individuals from all fields of physics, and European research institutions. As a learned society, the EPS engages in activities that strengthen ties among the physicists in Europe. As a federation of National Physical...

The interplay of spin and charge fluctuations in the random transverse-field Ising spin chain on the fermionic space is investigated. The finite chemical potential, which controls the charge fluctuations, leads to the appearance of the quantum critical region in the phase diagram where the magnetic correlations are quenched by nonmagnetic sites. Re...

Precise solutions of the stationary Fokker-Plank-type equation are obtained in quadratures for two- and three-dimensional electron gases. These solutions relate only to the case when electron-electron interaction is omitted. To illustrate our method we consider the example of the interaction of electrons with optical phonons at high temperatures wh...

A theory accounting for the specific features of magnetic polarons (MP) in the presence of spin glass order is presented. We derive and solve selfconsistent equations for i) the polaron magnetisation, ii) the thermodynamically averaged carrier--spin, and iii) for the spin glass order parameter. The temperature dependence of these quantities is anal...

The influence of the spin-glass phase formation of the (Cd,Mn)Te semi-magnetic layers on properties of the exciton magnetic polaron were investigated both theoretically and experimentally. The theoretical model offers a consistent description of the temperature dependence of the exciton magnetic polaron energy in the vicinity of spin-glass transiti...

A precise solution of the stationary one-dimensional Fokker-Planck-type equation is obtained in quadratures. The interaction of a one-dimensional electron gas with longitudinal-acoustic phonons and charged impurities is considered in detail. The nonequilibrium distribution functions of the gas are found and investigated in a wide range of electric...

Mikrofiche-Ausg.: 1 Mikrofiche : 24x. Würzburg, University, Diss., 1998.