Transport and shot noise measurements in YbRh₂Si₂ nano wires

The heavy fermion compound YbRh₂Si₂ exhibits a magnetic field-induced quantum critical point, between an antiferromagnetically ordered phase and a paramagnetic heavy Fermi liquid phase. Although the zero-field magnetic ordering temperature is only 70 mK, quantum critical non-Fermi liquid behavior persists over a broad temperature range, providing a wide parameter space to study the electron correlations in this “strange metal” system. Here we fabricate YbRh₂Si₂ nanowires using Ar dry etch, with chromium hard masks used to cover the designed pattern and removed by hydrochloric acid. The etched nanowires are examined by measuring magnetoresistance and comparing with those of the unpatterned original film, showing that the patterning does not degrade the material. We measure the shot noise in the nanowires and compared the signal in this non-Fermi liquid system with the shot noise in a conventional metal. We find suppressed shot noise in YbRh₂Si₂ nanowires, which is less than half of the noise in normal metal wires of comparable dimensions and resistance. We discuss this suppressed noise in the context of electron-electron interactions and the suggested lack of well-defined quasiparticles in strange metals.