arXiv subjects

M. Kiselev

Publications and source records attributed to M. Kiselev.

5 recordsLinked to original sources

arXiv2003

Explicit and Hidden Symmetries in Quantum Dots and Quantum Ladders

The concept of dynamical hidden symmetries in the physics of electron tunneling through composite quantum dots (CQD) and quantum ladders (QL) is developed and elucidated. Quite generally, dynamical symmetries are realizable in the space of low energy excited states in a given charge sector of nanoobjects, which involve spin variables and/or electron-hole pairs. While spin multiplets in an individual rung of a QL or in an isolated CQD form a representation space of the usual rotation group, this SU(2) symmetry is broken due to spin transfer (in QL) electron cotunneling through CQD. Dynamical symmetries in the space of spin multiplets are then unravelled in these processes. The corresponding symmetry groups are described by SO(n) or SU(n) depending on the origin of rotation group symmetry breaking. The effective spin Hamiltonians of QL and CQD are derived and expressed in terms of the pertinent group generators. We employ fermionization procedure for analyzing the physical content of these dynamical symmetries, including Kondo tunneling through CQD and Haldane gap formation in QL.

cond-mat↗

arXiv2003

Modulated replica symmetry breaking schemes for antiferromagnetic spin glasses

We define modulated replica symmetry breaking (RSB)-schemes which combine tree- and wave-like structures. A modulated scheme and unmodulated RSB are applied at 1-step level to a semiconductor model with antiferromagnetic Korenblit-Shender interaction. By comparison of the free energies we find evidence that a T=0 phase transition in the ferrimagnetic phase leads to a transition between the different RSB-schemes. An embedding factor of Parisi block matrices with sublattice-asymmetrical size is employed as a new variational parameter in the modulated scheme.

cond-mat.dis-nn↗

arXiv1999

Some aspects of electronic topological transition in 2D system on a square lattice. Excitonic ordered states

We study the ordered "excitonic" states which develop around the quantum critical point (QCP) associated with the electronic topological transition (ETT) in a 2D electron system on a square lattice. We consider the case of hopping beyond nearest neighbors when ETT has an unusual character. We show that the amplitude of the order parameter (OP) and of the gap in the electron spectrum increase with increasing the distance from the QCP, δ_c - δ, where δ= 1-n and "n" is an electron concentration. Such a behavior is different from the ordinary case when OP and the gap decrease when going away from the point which is a motor for instability. The gap opens at "hot spots" and extends untill the saddle points (SP) whatever is the doping concentration. The spectrum gets a characteristic flat shape as a result of hybrydization effect in the vicinity of two different SP's. The shape of the spectrum and the angle dependence of the gap have a striking similarity with the features observed in the normal state of the underdoped high-T$_c$ cuprates. We discuss also details about the phase diagram and the behaviour of the density of states.

cond-mat.supr-con↗

arXiv1999

Comment on "Theory of Unconventional Spin Density Wave: A Possible Mechanism of the Micromagnetism in U-based Heavy Fermion Compounds"

In the recent letter [1] by H. Ikeda and Y. Ohashi, a new, very attractive idea is proposed for the explanation of the micromagnetism in U-based heavy fermion compounds. For this sake a nontrivial spin density wave (d-SDW) is introduced. Our goal is to claim, that in the model considered, the mean-field analysis is incomplete: the ferromagnetic state missed by [1] overcomes d-SDW in a large region of the phase diagram (Fig.1 in [1]).

cond-mat.str-el↗

arXiv1999

New scenario for high-T_c cuprates: electronic topological transition as a motor for anomalies in the underdoped regime

We have discovered a new nontrivial aspect of electronic topological transition (ETT) in a 2D free fermion system on a square lattice. The corresponding exotic quantum critical point, δ=δ_c, T=0, (n=1-δis an electron concentration) is at the origin of anomalous behaviour in the interacting system on one side of ETT, δ<δ_c. The most important is an appearance of the line of characteristic temperatures, T^*(δ) \propto δ_c-δ. Application of the theory to high-T_c cuprates reveals a striking similarity to the observed experimentally behaviour in the underdoped regime (NMR and ARPES).

cond-mat.supr-con↗