Search results for "Fermion"
showing 10 items of 523 documents
Emulating Solid-State Physics with a Hybrid System of Ultracold Ions and Atoms
2013
We propose and theoretically investigate a hybrid system composed of a crystal of trapped ions coupled to a cloud of ultracold fermions. The ions form a periodic lattice and induce a band structure in the atoms. This system combines the advantages of scalability and tunability of ultracold atomic systems with the high fidelity operations and detection offered by trapped ion systems. It also features close analogies to natural solid-state systems, as the atomic degrees of freedom couple to phonons of the ion lattice, thereby emulating a solid-state system. Starting from the microscopic many-body Hamiltonian, we derive the low energy Hamiltonian including the atomic band structure and give an…
Composite Higgs bosons from neutrino condensates in an inverted see-saw scenario
2020
We present a realization of the idea that the Higgs boson is mainly a bound state of neutrinos induced by strong four-fermion interactions. The conflicts of this idea with the measured values of the top quark and Higgs boson masses are overcome by introducing, in addition to the right-handed neutrino, a new fermion singlet, which, at low energies, implements the inverse see-saw mechanism. The singlet fermions also develop a scalar bound state which mixes with the Higgs boson. This allows us to obtain a small Higgs boson mass even if the couplings are large, as required in composite scalar scenarios. The model gives the correct masses for the top quark and Higgs boson for compositeness scale…
Vortices in quantum droplets: Analogies between boson and fermion systems
2010
The main theme of this review is the many-body physics of vortices in quantum droplets of bosons or fermions, in the limit of small particle numbers. Systems of interest include cold atoms in traps as well as electrons confined in quantum dots. When set to rotate, these in principle very different quantum systems show remarkable analogies. The topics reviewed include the structure of the finite rotating many-body state, universality of vortex formation and localization of vortices in both bosonic and fermionic systems, and the emergence of particle-vortex composites in the quantum Hall regime. An overview of the computational many-body techniques sets focus on the configuration interaction …
Experimental Manifestations of Fermion Condensation in Strongly Correlated Fermi Systems
2019
Many strongly correlated Fermi systems including heavy-fermion (HF) metals and high-Tc superconductors belong to that class of quantum many-body systems for which the Landau–Fermi liquid theory fails. Instead, these systems exhibit non-Fermi-liquid properties that arise from violation of time-reversal (T) and particle– hole (C) invariance. Here we consider two most recent experimental puzzles, which cannot be explained neither within the Landau–Fermi liquid picture nor can they be made intelligible by the approaches like the Hubbard model and/or the Kondo effect, which are commonly used to spell out the typical non-Fermi-liquid behavior. The first experimental puzzle is the asymmetric (with…
Dynamics of heavy fermions: Drude response in and
2006
While the effective mass of heavy fermions governs their thermodynamics, the optical properties are dominated by the characteristic relaxation rate which is expected to scale inversely with the effective mass. At the relaxation rate clear features, the so-called Drude response occur in the real and imaginary parts of the complex conductivity. Conventional optical spectroscopy can only indirectly probe the Drude response; thus we use novel broadband microwave spectroscopy to directly measure the frequency-dependent conductivity of UPd2Al3 and UNi2Al3 in the relevant frequency range and unambiguously observe the full low-energy electrodynamics of the heavy fermions including the Drude respons…
Fermion Condensation in Strongly Interacting Fermi Liquids
2017
This article discusses the construction of a theory which is capable to explain so-called non-Fermi liquid behavior of strongly correlated Fermi systems. We show that such explanation can be done within the framework of a so-called fermion condensation approach. In this approach, as a result of fermion condensation quantum phase transition, ordinary Landau quasiparticles do not decay, but reborn, gaining new properties, as Phoenix from the ashes. The physical reason for that is altering of Fermi surface topology. To be more specific, in contrast to standard Landau paradigm stating that the quasiparticle effective mass does not depend on external stimuli like magnetic field and/or temperatur…
High Magnetic Fields Thermodynamics of Heavy Fermion Metals
2014
In this chapter, we present the comprehensive theoretical analysis of thermodynamics of HF compounds at high magnetic fields. Such analysis permits to gain a deeper insight into the interplay of high magnetic field and temperature in suppressing and retrieving the Landau Fermi liquid state in these substances. Our analysis shows that although high magnetic fields and temperatures alter the properties of ordinary Landau quasiparticles, they survive, generating the experimentally observable anomalies in the thermodynamical quantities of HF compounds. We illustrate our theoretical findings by the example of the HF compound \(\mathrm{{YbRh_2Si_2}}\).
Discriminating antiferromagnetic signatures in systems of ultracold fermions by tunable geometric frustration
2013
Recently, it has become possible to tune optical lattices continuously between square and triangular geometries. We compute thermodynamics and spin correlations in the corresponding Hubbard model using a determinant quantum Monte Carlo technique and show that the frustration effects induced by the variable hopping terms can be clearly separated from concomitant bandwidth changes by a proper rescaling of the interaction. An enhancement of the double occupancy by geometric frustration signals the destruction of nontrivial antiferromagnetic correlations at weak coupling and entropy $s\ensuremath{\lesssim}\mathrm{ln}(2)$ (and restores Pomeranchuk cooling at strong frustration), paving the way t…
Alloying-induced transition from local-moment to itinerant heavy fermion magnetism in Ce(Cu1−xNix)2Ge2
1990
Abstract A monotonous increase of the Kondo temperature in Ce(Cu1−xNix)2Ge2 from 7 (x = 0) to 30 K (x = 1) is accompanied by drastic changes of ground state properties: for x⩽0.2, a modulated magnetic structure (q01 = (0.28, 0.28, 0.54)) involving Kondo-reduced local Ce moments ( μ s = 0.74μ B Ce for x = 0) forms below TN1(x). TN1 = 4. 1 K for CeCu2Ge2 is strongly depressed upon increasing x. At x ≲ 0.2, a different modulation develops below TN2(x) which becomes maximum (≃4 K) for x = 0.5. Since this is characterized by a very small value of q02 (=(0, 0, 0.13) at x = 0.5) and a gradually decreasing ordered moment (reaching μs ≲ 0.2μB/Ce for x ⩾0.65), we ascribe it to “heavy fermion band mag…
Magnetic order in the heavy fermion system Ce(Cu1−xNix)2Ge2
1990
Abstract The magnetic phase diagram of the heavy fermion (HF) systems Ce(Cu 1−x Ni x ) 2 Ge 2 is discussed utilizing results of transport, thermodynamic and neutron-scattering measurements. While the Kondo temperature increases monotonically with x, a complex x-dependence is found for the Neel temperature, associated with a transition from local-moment to itinerant HF magnetism.