Tuning low-energy scales in YbRh${}_2$Si${}_2$ by non-isoelectronic substitution and pressure

Abstract

The heavy-fermion metal YbRh${}_2$Si${}_2$ realizes a field-induced quantum critical point with multiple vanishing energy scales $T_{\mathrm{N}}(B)$ and $T^{\ast }(B)$. We investigate their change with partial non-isoelectronic substitutions, chemical and hydrostatic pressure. Low-temperature electrical resistivity, specific heat and magnetic susceptibility of Yb(Rh${}_{1-x}$T${}_x$)${}_2$Si${}_2$ with T=Fe or Ni for $x\le 0.1$, magnetic fields $B\le 0.3$~T (applied perpendicular to the c-axis) and hydrostatic pressure $p\le 1.5$~GPa are reported. The data allow to disentangle the combined influences of hydrostatic and chemical pressure, as well as non-isoelectronic substitution. In contrast to Ni- and Co-substitution, which enhance magnetic order, Fe-substitution acts oppositely. For $x=0.1$ it also completely suppresses the $T^{\ast }$ crossover and eliminates ferromagnetic fluctuations. The pressure, magnetic field and temperature dependences of $T^{\ast }$ are incompatible with its interpretation as Kondo breakdown signature.

25 pages including supplemental material; accepted for publication in Phys. Rev. Research