Temperature-dependent spectral function of a Kondo impurity in ans-wave superconductor

Abstract

Using the numerical renormalization group method, the effect due to a Kondo impurity in an swave superconductor is examined at finite temperature (T ). The T -behaviors of the spectral function and the magnetic moment at the impurity site are calculated. At T =0, the spin due to the impurity is in singlet state when the ratio between the Kondo temperature T k and the superconducting gap ∆(0) is larger than 0.26. Otherwise, the spin of the impurity is in a doublet state. We show that the separation of the double Yu-Shiba-Rusinov peaks in the spectral function shrinks as T increases if T k /∆(0) < 0.26 while it is expanding if T k /∆(0) > 0.26 and ∆(0) remains to be a constant. These features could be measured by experiments and thus provide a unique way to determine whether the spin of the single Kondo impurity is in singlet or doublet state at zero temperature.

Renormalization approach to the superconducting Kondo model

“…In agreement with the numerical results from Ref. [6] we find a characteristic temperature effect where in the YSR regime the bound state energy is shifted to smaller values. This effect becomes inverted in the Kondo regime where the shift is smaller but the energy increases with temperature.…”

“…In all regimes ω 0 approaches the value of the classical spin case in the limit of large S. (b) Variation of the temperature. In agreement with former numerical studies[6] the YSR state energy decreases with temperature while in the Kondo regime it slightly increases.…”

“…The energy of the second YSR excitation at −ω 0 is also shown (red line). One clearly recognizes the behavior known from former numerical studies [6,27] including the crossing at ω 0 = 0 (dashed line) which marks the transition from a weak coupling regime at low T K to a strong coupling regime at larger T K where the Kondo physics becomes significant. Our numerical solution shows that the strong coupling regime is characterized by a singularity in the renormalized exchange coupling Jk .…”

“…The study of bound states at low temperature has become important for the understanding of the interaction between impurities and electronic properties of the underlying correlated material. An important example in this context is a magnetic impurity which interacts with a superconducting condensate leading to competition between the Yu-Shiba-Rusinov (YSR) bound states [1][2][3] and the Kondo physics [4][5][6]. Depending on the strength of the exchange coupling a transition from a regime with weakly coupled YSR states to a Kondo singlet state is found [7][8][9].…”

Picosecond ionization dynamics in femtosecond filaments at high pressures

“…We believe this effect exists at lower pressure for longer pulse durations. Ultimately, these results are important for characterizing impact ionization and excitation in the presence of the laser field [33] and for those experiments that involve multiple time-delayed pulses for filament and ionization control [34][35][36], in particular at high pressures or at mid-infrared wavelengths.…”