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TT: Fachverband Tiefe Temperaturen

TT 56: CE: Heavy Fermions

TT 56.5: Talk

Thursday, March 17, 2011, 17:30–17:45, HSZ 105

Magnetic ac susceptibility of YbRh₂Si₂ at ultra-low temperatures — •Lucia Steinke^1,2, Erwin Schuberth², Stefan Lausberg¹, Christoph Klingner¹, Cornelius Krellner¹, Manuel Brando¹, Christoph Geibel¹, and Frank Steglich¹ — ¹Max-Planck-Institut für Chemische Physik fester Stoffe, 01187 Dresden, Germany — ²Walther Meissner Institut, 85748 Garching, Germany

Recent magnetization measurements on the heavy fermion compound YbRh₂Si₂ at ultra-low temperatures (ULT) below 1 mK show that the weak antiferromagnetic phase, which forms at B=0 below T_N=70 mK, is not the T=0 ground state of the system. Instead, two additional ULT regimes were discovered [1]: a new phase below T_A = 2.2 mK, where the phase transition is observed as a pronounced magnetization peak, and a second regime below T_B =15 mK, where zero-field-cooled / field-cooled measurements begin to show a hysteresis. To clarify the origin of these two new ULT regimes, particularly to seek evidence for possible superconducting states in YbRh₂Si₂, we measured the magnetic ac susceptibility at B=0. Initial results indicate a decrease in the real part χ′ of the ac susceptibility as the sample temperature is lowered beyond T_B = 15 mK and a pronounced drop in χ′ as T drops below the transition temperature T_A = 2.2 mK. Whether the response is indeed diamagnetic depends on the yet unknown background signal.
E. Schuberth et al., J. Phys. C 150, 042178 (2009)