Quantum criticality in sub-Ohmic systems with three competing terms: beyond conventional spin-boson physics

• URL: http://arxiv.org/abs/2603.07031v1
• Date: Sat, 07 Mar 2026 04:27:39 GMT
• Title: Quantum criticality in sub-Ohmic systems with three competing terms: beyond conventional spin-boson physics
• Abstract summary: Quantum phase transitions (QPTs) in the spin-boson model with/without the rotating-wave approximation (RWA) are investigated.<n>Four cases involving different system-environment interactions are examined.<n>A rich phase diagram is revealed in the tunneling-coupling plane even at the low spectral exponents $s1/2$, with a novel U(1)-symmetric phase being identified.
• Score: 24.555358456958814
• License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/
• Abstract: Quantum phase transitions (QPTs) in the spin-boson model with/without the rotating-wave approximation (RWA) are systematically investigated through variational calculations using a sub-Ohmic bath with high spectral density. Four cases involving different system-environment interactions are examined, where transition points and critical exponents are accurately determined across varying tunneling strengths. Contrary to prior work, a rich phase diagram is revealed in the tunneling-coupling plane even at the low spectral exponent $s<1/2$, with a novel U(1)-symmetric phase being identified. As coupling increases, a multi-stage QPT sequence arises for the tunneling $0<Δ< Δ^*=0.074(1)$, whereas a single transition occurs beyond this range. Furthermore, an odd-parity phase is found to emerge even under the positive tunneling, exhibiting distinct characteristics relative to the prototype model.

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