Conduction electron spin resonance in the α-Yb1-xFexAlB4 (0 ⩽ x ⩽ 0.50) and α-LuAlB4 compounds

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Critical Phenomena

Background:

• β-YbAlB4 is a studied heavy fermion system, notable for its superconductivity emerging from a non-Fermi liquid (NFL) state near quantum criticality.
• It exhibits a unique electron spin resonance (ESR) signal that transitions from conduction electron spin resonance (CESR) at high temperatures to Kondo quasiparticles spin resonance (KQSR) at low temperatures.
• The α-YbAlB4 phase, a structural variant, is a paramagnetic Fermi liquid (FL) but may exhibit NFL behavior with Fe doping.

Purpose of the Study:

• To investigate the electron spin resonance (ESR) properties of the α-Yb1-xFexAlB4 series.
• To determine if the α-phase can exhibit NFL behavior or magnetic ordering upon Fe doping.
• To understand the conditions necessary for the emergence of the Kondo quasiparticles spin resonance (KQSR) signal.

Main Methods:

• Electron Spin Resonance (ESR) studies were performed on α-Yb1-xFexAlB4 (0 ≤ x ≤ 0.50) and α-LuAlB4.
• Measurements were conducted across a temperature range of 10 K to 300 K.
• The observed ESR signals were analyzed and compared to those of β-YbAlB4.

Main Results:

• The ESR signal in all measured α-Yb1-xFexAlB4 samples consistently behaved as CESR across the entire temperature range.
• This is in stark contrast to the β-YbAlB4 system, which displays temperature-dependent ESR features (CESR to KQSR).
• The absence of the KQSR signal in the α-phase suggests it is not in proximity to a quantum critical point.

Conclusions:

• The presence of the Kondo quasiparticles spin resonance (KQSR) signal is strongly dependent on the proximity to a quantum critical point.
• The α-YbAlB4 system, even with Fe doping, does not appear to reach the critical regime necessary for KQSR.
• This highlights the unique electronic state and quantum criticality associated with the β-YbAlB4 heavy fermion superconductor.