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ABSTRACT: We show that near a quantum critical point generating quantum criticality of
strongly correlated metals where the density of electron states diverges, the
quasi-classical physics remains applicable to the description of the
resistivity \rho of strongly correlated metals due to the presence of a
transverse zero-sound collective mode, reminiscent of the phonon mode in
solids. We demonstrate that at T, being in excess of an extremely low Debye
temperature T_D, the resistivity \rho(T) changes linearly with T, since the
mechanism, forming the T dependence of \rho(T), is the same as the
electron-phonon mechanism that prevails at high temperatures in ordinary
metals. Thus, electron-phonon scattering leads to near material-independence of
the lifetime \tau of quasiparticles that is expressed as the ratio of the
Planck constant \hbar to the Boltzmann constant k_B, T\tau\sim \hbar/k_B. We
find that at T<T_D there exists a different mechanism, maintaining the T-linear
dependence of \rho(T), and making the constancy of \tau fail in spite of the
presence of T-linear dependence. Our results are in good agreement with
exciting experimental observations.
04/2013;
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ABSTRACT: Extraordinary new materials named quasicrystals and characterized by
noncrystallographic rotational symmetry and quasiperiodic translational
properties have attracted scrutiny. Study of quasicrystals may shed light on
the most basic notions related to the quantum critical state observed in
heavy-fermion metals. We show that the electronic system of some quasicrystals
is located at the fermion condensation quantum phase transition without tuning.
In that case the quasicrystals possess the quantum critical state with the
non-Fermi liquid behavior which in magnetic fields transforms into the Landau
Fermi-liquid one. Remarkably, the quantum critical state is robust despite the
strong disorder experienced by the electrons. We also demonstrate for the first
time that quasicrystals exhibit the typical scaling behavior of their
thermodynamic properties such as the magnetic susceptibility, and belong to the
famous family of heavy-fermion metals. Our calculated thermodynamic properties
are in good agreement with recent experimental observations.
02/2013;
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ABSTRACT: Understanding the nature of field-tuned metamagnetic quantum criticality in
the ruthenate Sr3Ru2O7 has presented a significant challenge within condensed
matter physics. Attention has centered on the role of quantum criticality in
the formation of an ordered phase existing within a restricted range of
magnetic fields B at low temperatures T. It is known from experiments that the
entropy within the ordered phase forms a peak, and is unexpectedly higher than
that outside, while the magnetoresistivity experiences steep jumps near the
ordered phase, with a step-like growth culminating in a peak and followed by a
similarly abrupt drop. Data collected on Sr3Ru2O7 allow us to provide
qualitative insights into the critical regime and its quantum critical points
(QCPs) obscured by the ordered phase. We find a challenging connection between
Sr3Ru2O7 and heavy-fermion metals expressing universal physics that transcends
microscopic details. Our construction of the T-B phase diagram of Sr3Ru2O7
permits us to explain main features of the experimental one, and unambiguously
implies an interpretation of its extraordinary low-temperature thermodynamic in
terms of fermion condensation quantum phase transition leading to the formation
of a flat band at the restricted range of magnetic fields B. We show that it is
the flat band that generates both the entropy peak and irregular residual
resistivity jumps at the QCPs. Therefore, the magnetoresistivity jumps and its
variation through the peak are defined by the variation of the irregular
residual resistivity, and exhibit the spectacular independence of temperature.
11/2012;
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ABSTRACT: Strongly correlated Fermi systems are among the most intriguing and
fundamental systems in physics. We show that the herbertsmithite ZnCu3(OH)6Cl2
can be viewed as a new type of strongly correlated electrical insulator that
possesses properties of heavy-fermion metals with one exception: it resists the
flow of electric charge. We demonstrate that herbertsmithite's low temperature
properties are defined by a strongly correlated quantum spin liquid made with
such hypothetic particles as fermionic spinons which carry spin 1/2 and no
charge. Our calculations of its thermodynamic and relaxation properties are in
good agreement with recent experimental facts and allow us to reveal their
scaling behavior which strongly resembles that observed in heavy-fermion
metals. Analysis of the dynamic magnetic susceptibility of strongly correlated
Fermi systems suggests that there exist at least two types of its scaling.
10/2012;
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ABSTRACT: Physicists are engaged in vigorous debate on the nature of the quantum
critical points (QCP) governing the low-temperature properties of heavy-fermion
(HF) metals. Recent experimental observations of the much-studied compound
YbRh2Si2 in the regime of vanishing temperature incisively probe the nature of
its magnetic-field-tuned QCP. The jumps revealed both in the residual
resistivity rho_0 and the Hall resistivity R_H, along with violation of the
Wiedemann-Franz law, provide vital clues to the origin of such non-Fermi-liquid
behavior. The empirical facts point unambiguously to association of the
observed QCP with a fermion-condensation phase transition. Based on this
insight, the resistivities rho_0 and R_H are predicted to show jumps at the
crossing of the QCP produced by application of a magnetic field, with attendant
violation of the Wiedemann-Franz law. It is further demonstrated that
experimentally identifiable multiple energy scales are related to the scaling
behavior of the effective mass of the quasiparticles responsible for the
low-temperature properties of such HF metals.
07/2012;
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06/2012;
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ABSTRACT: We present a theory of the dynamic magnetic susceptibility of quantum spin
liquid. The obtained results are in good agreement with experimental facts
collected on herbertsmithite ZnCu3(OH)6Cl2 and on heavy-fermion metals, and
allow us to predict a new scaling in magnetic fields in the dynamic
susceptibility. Under the application of strong magnetic fields quantum spin
liquid becomes completely polarized. We show that this polarization can be
viewed as a manifestation of gapped excitations when investigating the
spin-lattice relaxation rate.
06/2012;
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ABSTRACT: An explanation of paradoxical behavior of the residual resistivity rho_0 of
the heavy-fermion metal CeCoIn5 in magnetic fields and under pressure is
developed. The source of this behavior is identified as a flattening of the
single-particle spectrum, which exerts profound effects on the specific heat,
thermal expansion coefficient, and magnetic susceptibility in the normal state,
the specific heat jump at the point of superconducting phase transition, and
other properties of strongly correlated electron systems in solids. It is shown
that application of a magnetic field or pressure to a system possessing a flat
band leads to a strong suppression of rho_0. Analysis of its measured
thermodynamic and transport properties yields direct evidence for the presence
of a flat band in CeCoIn5.
06/2012;
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ABSTRACT: The single-particle spectrum and momentum distribution of quasiparticles in a cold dense quark-gluon plasma are calculated
within the Fermi liquid approach. It is shown that this system does not behave as a standard Fermi liquid: at zero temperature,
the single-particle spectrum has a plateau at the Fermi surface, while the Fermi surface itself has a nonzero volume in momentum
space.
Physics of Atomic Nuclei 04/2012; 72(8):1382-1389. · 0.57 Impact Factor
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ABSTRACT: Renewed interest in 3He physics has been stimulated by experimental observation of non-Fermi-liquid behavior of dense 3He films at low temperatures. Abnormal behavior of the specific heat C(T) of two-dimensional liquid 3He is demonstrated in the occurrence of a T-independent term in C(T). To uncover the origin of this phenomenon, we have considered the group velocity of transverse zero sound propagating in
a strongly correlated Fermi liquid. For the first time, it is shown that if two-dimensional liquid 3He is located in the vicinity of the quantum critical point associated with a divergent quasiparticle effective mass, the
group velocity depends strongly on temperature and vanishes as T is lowered toward zero. The predicted vigorous dependence of the group velocity can be detected in experimental measurements
on liquid 3He films. We have demonstrated that the contribution to the specific heat coming from the boson part of the free energy due
to the transverse zero-sound mode follows the Dulong-Petit Law. In the case of two-dimensional liquid 3He, the specific heat becomes independent of temperature at some characteristic temperature of a few millikelvins.
JETP Letters 04/2012; 92(8):532-536. · 1.35 Impact Factor
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ABSTRACT: Competing scenarios for quantum critical points (QCPs) of strongly interacting Fermi systems signaled by a divergent density
of states at zero temperature are contrasted. The conventional scenario, which enlists critical fluctuations of a collective
mode and attributes the divergence to a coincident vanishing of the quasi-particle strength z, is shown to be incompatible with identities arising from conservation laws prevailing in the fermionic medium. An alternative
scenario, in which the topology of the Fermi surface is altered at the QCP, is found to explain the non-Fermi-liquid thermodynamic
behavior observed experimentally in Yb-based compounds close to the QCP. It is suggested that combination of the topological
scenario with the theory of quantum phase transitions will provide a proper foundation for analysis of the extended QCP region.
JETP Letters 04/2012; 90(9):628-632. · 1.35 Impact Factor
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ABSTRACT: A system of interacting, identical fermions described by standard Landau
Fermi-liquid (FL) theory can experience a rearrangement of its Fermi surface if
the correlations grow sufficiently strong, as occurs at a quantum critical
point where the effective mass diverges. As yet, this phenomenon defies full
understanding, but salient aspects of the non-Fermi-liquid (NFL) behavior
observed beyond the quantum critical point are still accessible within the
general framework of the Landau quasiparticle picture. Self-consistent
solutions of the coupled Landau equations for the quasiparticle momentum
distribution $n(p)$ and quasiparticle energy spectrum $\epsilon(p)$ are shown
to exist in two distinct classes, depending on coupling strength and on whether
the quasiparticle interaction is regular or singular at zero momentum transfer.
One class of solutions maintains the idempotency condition $n^2(p)=n(p)$ of
standard FL theory at zero temperature $T$ while adding pockets to the Fermi
surface. The other solutions are characterized by a swelling of the Fermi
surface and a flattening of the spectrum $\epsilon(p)$ over a range of momenta
in which the quasiparticle occupancies lie between 0 and 1 even at T=0. The
latter, non-idempotent solution is revealed by analysis of a Poincar\'e mapping
associated with the fundamental Landau equation connecting $n(p)$ and
$\epsilon(p)$ and validated by solution of a variational condition that yields
the symmetry-preserving ground state. Paradoxically, this extraordinary
solution carries the burden of a large temperature-dependent excess entropy
down to very low temperatures, threatening violation of the Nernst Theorem. It
is argued that certain low-temperature phase transitions offer effective
mechanisms for shedding the entropy excess. Available measurements in
heavy-fermion compounds provide concrete support for such a scenario.
03/2012;
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ABSTRACT: A Comment on the Letter by Andreas Hackl and Matthias Vojta, Phys. Rev. Lett. 106, 137002 (2011). The authors of the Letter offer a Reply.
Physical Review Letters 12/2011; 107(27):279701; author reply 279702. · 7.37 Impact Factor
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Physical Review Letters 12/2011; 107:279701. · 7.37 Impact Factor
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ABSTRACT: A topological crossover, associated with the collapse of the Fermi surface in
strongly correlated Fermi systems, is examined. It is demonstrated that in
these systems, the temperature domain where standard Fermi liquid results hold
dramatically narrows, because the Landau regime is replaced by a classical one.
The impact of the collapse of the Fermi surface on pairing correlations is
analyzed. In the domain of the Lifshitz phase diagram where the Fermi surface
collapses, splitting of the BCS superconducting phase transition into two
different ones of the same symmetry is shown to occur.
08/2011;
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ABSTRACT: A quasiparticle pattern advanced in Landau's first article on Fermi liquid
theory is adapted to elucidate the properties of a class of strongly correlated
Fermi systems characterized by a Lifshitz phase diagram featuring a quantum
critical point (QCP) where the density of states diverges. The necessary
condition for stability of the Landau Fermi Liquid state is shown to break down
in such systems, triggering a cascade of topological phase transitions that
lead, without symmetry violation, to states with multi-connected Fermi
surfaces. The end point of this evolution is found to be an exceptional state
whose spectrum of single-particle excitations exhibits a completely flat
portion at zero temperature. Analysis of the evolution of the temperature
dependence of the single-particle spectrum yields results that provide a
natural explanation of classical behavior of this class of Fermi systems in the
QCP region.
08/2011;
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ABSTRACT: We study the temperature evolution of the single-particle spectrum
$\epsilon(p)$ and quasiparticle momentum distribution $n(p)$ of homogeneous
strongly correlated Fermi systems beyond a point where the necessary condition
for stability of the Landau state is violated, and the Fermi surface becomes
multi-connected by virtue of a topological crossover. Attention is focused on
the different non-Fermi-liquid temperature regimes experienced by a phase
exhibiting a single additional hole pocket compared with the conventional
Landau state. A critical experiment is proposed to elucidate the origin of NFL
behavior in dense films of liquid $^3$He.
05/2011;
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ABSTRACT: The low-temperature kinetics of the strongly correlated electron liquid inhabiting a solid is analyzed. It is demonstrated that a softly damped branch of transverse zero sound emerges when several bands cross the Fermi surface simultaneously near a quantum critical point at which the density of states diverges. Suppression of the damping of this branch occurs due to a mechanism analogous to that affecting the phonon mode in solids at room temperature, giving rise to a classical regime of transport at extremely low temperatures in the strongly correlated Fermi system. Comment: 4 pages
10/2010;
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ABSTRACT: Motivated by recent observations of C4 symmetry breaking in strongly correlated two-dimensional electron systems on a square lattice, we analyze this phenomenon within an extended Fermi-liquid approach. It is found that the symmetry violation is triggered by a continuous topological phase transition associated with exchange of antiferromagnetic fluctuations. In contrast to predictions of mean-field theory, the structure of a part of the single-particle spectrum violating C4 symmetry is found to be highly anisotropic, with a peak located in the vicinity of saddle points.
Phys. Rev. B. 09/2010; 82(12).
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ABSTRACT: The Fermi liquid approach is applied to the problem of spontaneous violation
of the four-fold rotational point-group symmetry ($C_4$) in strongly correlated
two-dimensional electronic systems on a square lattice. The symmetry breaking
is traced to the existence of a topological phase transition. This continuous
transition is triggered when the Fermi line, driven by the quasiparticle
interactions, reaches the van Hove saddle points, where the group velocity
vanishes and the density of states becomes singular. An unconventional Fermi
liquid emerges beyond the implicated quantum critical point.
04/2010;
