Evolution of the Kondo lattice and non-Fermi liquid excitations in a heavy-fermion metal

Abstract

Strong electron correlations can give rise to extraordinary properties of metals with renormalized Landau quasiparticles. Near a quantum critical point, these quasiparticles can be destroyed and non-Fermi liquid behavior ensues. YbRh2Si2 is a prototypical correlated metal exhibiting the formation of quasiparticle and Kondo lattice coherence, as well as quasiparticle destruction at a field-induced quantum critical point. Here we show how, upon lowering the temperature, Kondo lattice coherence develops at zero field and finally gives way to non-Fermi liquid electronic excitations. By measuring the single-particle excitations through scanning tunneling spectroscopy, we find the Kondo lattice peak displays a non-trivial temperature dependence with a strong increase around 3.3 K. At 0.3 K and with applied magnetic field, the width of this peak is minimized in the quantum critical regime. Our results demonstrate that the lattice Kondo correlations have to be sufficiently developed before quantum criticality can set in.

Flat bands and strongly correlated Fermi systems

“…This behavior has been observed in recent measurements of tunneling conductivity on both YbRh 2 Si 2 [5,6] and graphene [7]. Our analysis of the data [6,7] demonstrates that indeed the application of magnetic field restores the symmetry of the differential conductivity.…”

“…An important point here is that the application of magnetic field B restores the normal Fermi-liquid properties so that the above mentioned conductivity becomes a symmetric function of V due to the reappearance of the Tand C-invariances [2,13,14]. This behavior has been observed in recent measurements of tunneling conductivity on both YbRh 2 Si 2 [5,6] and graphene [7]. Our analysis of the data [6,7] demonstrates that indeed the application of magnetic field restores the symmetry of the differential conductivity.…”

“…As we have seen above, the asymmetry of the tunneling conductivity vanishes in the LFL state [2,[13][14][15]. Figure 3 shows the differential conductivity σ d observed in measurements on YbRh 2 Si 2 [5,6]. It is seen that its asymmetry diminishes at elevating magnetic field B, for the minima of the curves shift to the V = 0 point, see Fig.…”

“…However the experimental studies of HF metals and HTSC are difficult since the corresponding critical points are usually concealed in the presence of the other phase transitions like the antiferromagnetic (AF) and/or superconducting. Recently the challenging properties of tunneling conductivity manifesting themselves in the presence magnetic field were observed in a graphene with a flat band [7] as well as in HTSC and YbRh 2 Si 2 HF metal [5,6]. Studying and analyzing these properties will shed light on the nature of the quantum phase transition in these substances.…”

“…The difference is that fermions to condense, the Fermi surface should change its topology [1-4], leading to violation of time-reversal (T) and particle-hole (C) symmetries. Thus, the famous Landau theory of Fermi liquids does not work for the systems with fermion condensate (FC) so that several experimentally observable anomalies have not been explained so far.Here we use FC approach to explain recent observations of the asymmetric tunneling conductivity in heavy-fermion compounds and graphene [5][6][7] and its restoration in magnetic fields, as well as the violation of Leggett theorem [8,9], recently observed experimentally [10,11] in overdoped cuprates, and recent observation of the challenging universal scaling connecting linear-T -dependent resistivity to the superconducting superfluid density [12].…”