Nonanalytic Magnetic Response of Fermi- and non-Fermi Liquids

We present the expression for the quasiparticle vertex function $\Gamma^{\omega }(K_{F},P_{F})$ (proportional to the Landau function) in a 2D Fermi liquid (FL) near a $T=0$ instability towards antiferromagnetism. Previous studies have found that near an instability, the system enters into a critical FL regime, in which the fermionic self-energy is large near hot spots (points on the Fermi surface connected by the antiferromagnetic ordering vector $q_\pi=(\pi,\pi)$) and has mu...

We consider the non-analytic terms in the spin susceptibility arising as a result of rescaterring of pairs of quasiparticles. We emphasize the importance of rescattering in the Cooper channel for the analysis of the temperature dependences in the two-dimensional electron systems in the ballistic regime. In the calculation of the linear in $T$ term we use angular harmonics in the Cooper channel, because for each harmonic the interaction amplitude is renormalized independently....

We measure the magnetic susceptibility of a Fermi gas with tunable interactions in the low-temperature limit and compare it to quantum Monte Carlo calculations. Experiment and theory are in excellent agreement and fully compatible with the Landau theory of Fermi liquids. We show that these measure- ments shed new light on the nature of the excitations of the normal phase of a strongly interacting Fermi gas.

We describe a minimal model, based on a spin only Hamiltonian with a single energy scale for itinerant electron metamagnetism. Within this model the metamagnetic critical field is directly proportional to the temperature where a peak in the linear susceptibility occurs which in turn is related in a simple manner to the temperature where the nonlinear susceptibilities also peak. The spin dependent thermodynamic properties are derived in a straightforward manner and bear a stri...

We revisit the issue of the leading nonanalytic corrections to the temperature dependence of the specific heat coefficient, $\gamma (T)=C(T)/T,$ for a system of interacting fermions in three dimensions. We show that the leading temperature dependence of the specific heat coefficient $\gamma (T)-\gamma (0) \propto T^3 \ln T$ comes from two physically distinct processes. The first process involves a thermal excitation of a single particle-hole pair, whose components interact vi...

We study a mean-field model of a Kondo alloy using numerical techniques and analytic approximations. In this model, randomly distributed magnetic impurities interact with a band of conduction electrons and have a residual RKKY coupling of strength $J$. This system has a quantum critical point at $J=J_{c} \sim T_{K}^0$, the Kondo scale of the problem. The $T$ dependence of the spin susceptibility near the quantum critical point is singular with $\chi(0)-\chi(T) \propto T^{\gam...

We investigate the specific heat and magnetisation of a ferrimagnet with gS=1 and S=1/2 spins in a finite magnetic field using the transfer matrix DMRG down to T=0.025J. Ferromagnetic gapless and antiferromagnetic gapped excitations for H=0 lead to rich thermodynamics for H > 0. While the specific heat is characterized by a generic double peak structure, magnetisation reveals two critical fields, Hc1=1.76(1) and Hc2=3.00(1) with square-root behaviour in the T=0 magnetisation....

In this work we revisit itinerant ferromagnetism in 2D and 3D electron gases with arbitrary spin-orbit splitting and strong electron-electron interaction. We identify the resonant scattering processes close to the Fermi surface that are responsible for the instability of the ferromagnetic quantum critical point at low temperatures. In contrast to previous theoretical studies, we show that such processes cannot be fully suppressed even in presence of arbitrary spin-orbit split...

We establish the consistency of the Fermi liquid description and find a relation between Fermi liquid constants for the two dimensional electron system near the point of full polarization due to a parallel magnetic field $H$. Our results enable us to predict connections between different thermodynamic properties of the system. In particular, we find that near the point of full polarization $H_c$, the thermodynamic compressibility of the system experiences a jump with the subl...

We study the spin-glass transition in a disordered quantum model. There is a region in the phase diagram where quantum effects are small and the phase transition is second order, as in the classical case. In another region, quantum fluctuations drive the transition first order. Across the first order line the susceptibility is discontinuous and shows hysteresis. Our findings reproduce qualitatively observations on LiHo$_x$Y$_{1-x}$F$_4$. We also discuss a marginally stable sp...