Exotic States Found in Complex Quantum Systems

Scientists are increasingly investigating the interplay between non-Fermi liquid behaviour and non-Hermitian physics in condensed matter systems, and the multichannel Kondo model provides a crucial platform for exploring these exotic collective phenomena. Wei-Zhu Yi, Yun Chen, and Jun-Jun Pang, working with colleagues Hong Chen, Baigeng Wang, and Rui Wang, all from the National Laboratory of Solid State Microstructures and Department of Physics at Nanjing University, present a comprehensive study of this model, proposing an experimental configuration to achieve precise channel symmetry and controllable PT symmetry. Their multi-method approach, combining the Bethe ansatz, numerical renormalization group calculations, and boundary conformal field theory, identifies a Yu-Shiba-Rusinov-like state and reveals anomalous temperature dependence in Kondo conductance, significantly advancing our understanding of non-Hermitian quantum systems beyond conventional Hermitian models. Scientists are increasingly exploring physics beyond standard models to unlock novel material properties. Understanding systems where energy is not conserved, known as non-Hermitian physics, could revolutionise areas from electronics to quantum technologies. This work establishes a pathway to observe and control these exotic effects, potentially paving the way for entirely new devices. Researchers have unveiled a new understanding of how quantum systems behave when strongly interacting and subject to non-Hermitian effects, a departure from traditional quantum mechanics that allows for energy loss or gain. This work focuses on the non-Hermitian multichannel Kondo model, a complex system exhibiting both non-Fermi liquid behaviour and non-Hermitian physics, offering a unique platform to explore exotic quantum phenomena. They have successfully proposed an experimental configuration capable of realising this model with precise control over channel symmetry and PT symmetry, a concept relating to symmetry under combined parity and time reversal. The study employs a combination of theoretical techniques, including the Bethe ansatz, numerical renormalization group calculations, and boundary conformal field theory, to investigate the model’s low-energy spectrum, thermodynamic properties, and transport characteristics. A key discovery is the identification of a Yu-Shiba-Rusinov-like state, previously observed in simpler non-Hermitian systems, now appearing within this more intricate multichannel framework. Numerical simulations confirm the emergence of this state under conditions of relatively strong non-Hermiticity within the PT-asymmetric model, providing crucial validation of theoretical predictions. Furthermore, the application of boundary conformal field theory to the PT-symmetric model reveals an unusual temperature dependence of the Kondo conductance, a measure of electrical conductivity, deviating from the behaviour expected in conventional Hermitian systems. This anomalous behaviour suggests a fundamentally different mechanism governing electron transport in these non-Hermitian correlated systems. The research not only deepens our understanding of non-Fermi liquid physics but also opens avenues for exploring novel quantum phenomena and potentially designing new materials with tailored electronic properties. This multi-method approach establishes a robust framework for investigating correlated non-Hermitian systems, paving the way for future studies of more complex quantum materials and devices. Yu-Shiba-Rusinov state and anomalous Kondo conductance in a non-Hermitian multichannel system The research details a non-Hermitian multichannel Kondo model exhibiting both non-Fermi liquid and non-Hermitian physics, revealing a Yu-Shiba-Rusinov-like state in the relatively strong non-Hermiticity regime of a PT-asymmetric model. Bethe ansatz calculations identified the existence of this state, previously observed in the non-Hermitian single-channel Kondo model, confirming its presence within the multichannel system. Subsequent non-Hermitian numerical renormalization group calculations provided clear numerical signatures of the Yu-Shiba-Rusinov state, solidifying its emergence under conditions of significant non-Hermiticity. Boundary conformal field theory analysis of the PT-symmetric model uncovered an anomalous temperature dependence of the Kondo conductance, diverging from the behaviour expected in conventional Hermitian Kondo systems. Specifically, around the weak-coupling fixed point, the impurity moment decouples from conduction electrons even with antiferromagnetic Kondo couplings, resulting in a universal low-temperature conductance proportional to 1/ln2(T/TK). This decoupling arises from a non-Hermitian induced mechanism, distinct from the dissipation observed in underscreened Kondo models. Around the strong-coupling fixed point, the boundary conformal field theory predicts an anomalous deviation in the Kondo conductance as temperature increases. This non-Hermiticity-enriched anomaly originates from an emergent boundary conformal field theory featuring non-Hermitian boundary operators, unique to systems displaying both non-Hermiticity and non-Fermi liquid characteristics. Perturbative renormalization group calculations suggested two possible phases corresponding to weak and strong coupling fixed points, while the non-Hermitian numerical renormalization group method clarified the role of PT symmetry by considering both PT-symmetric and PT-asymmetric configurations. A realistic setup utilising quantum-dot-assisted tunneling junctions with Majorana fermions is proposed to experimentally realise the non-Hermitian multichannel Kondo model, demonstrating a step-by-step implementation scheme. Theoretical modelling and experimental realisation of PT-symmetric Kondo physics A Bethe ansatz approach initially established the theoretical groundwork by identifying the existence of a Yu-Shiba-Rusinov-like state, a localized magnetic moment screened by conduction electrons, within the non-Hermitian single-channel Kondo model. Subsequently, non-Hermitian numerical renormalization group calculations were performed to confirm the emergence of this state in the PT-asymmetric multichannel Kondo model under conditions of relatively strong non-Hermiticity. The NRG method, a technique for iteratively diagonalizing increasingly larger effective Hamiltonians, allowed for detailed mapping of the low-energy spectrum and associated thermodynamic properties. Researchers devised an experimental setup intended to realise the non-Hermitian multichannel Kondo model with both exact channel symmetry and controllable PT symmetry, crucial for isolating and studying the interplay between non-Fermi liquid behaviour and non-Hermitian physics. Boundary conformal field theory was then applied to the PT-symmetric model, providing a framework to analyse the system’s behaviour at low energies and large length scales. This theoretical framework enabled the prediction of an anomalous temperature dependence of the Kondo conductance, a measure of electron transport through the impurity, differing from the expected behaviour in conventional Hermitian Kondo systems. The combination of analytic Bethe ansatz, numerical NRG, and boundary conformal field theory provides a robust and multifaceted investigation of the model’s properties, addressing both ground state characteristics and dynamic transport phenomena. Non-Hermitian physics unlocks control of Kondo interactions in engineered quantum systems Scientists are increasingly turning to non-Hermitian physics, systems that defy conventional symmetry rules, as a means of modelling complex quantum phenomena. This work offers a significant step forward by demonstrating a controllable experimental platform for exploring the interplay between non-Hermitian effects and the Kondo problem, a long-studied puzzle in condensed matter physics concerning the behaviour of magnetic impurities within conducting materials. The difficulty has always been creating systems where these subtle effects can be isolated and precisely measured, but the proposed setup, utilising carefully engineered multichannel configurations, appears to overcome this hurdle. The implications extend beyond fundamental quantum mechanics, potentially impacting fields like spintronics and quantum computing. The identification of a Yu-Shiba-Rusinov-like state, previously observed in simpler non-Hermitian systems, within this more complex model is particularly noteworthy, suggesting that these exotic states are robust and may appear in a wider range of physical scenarios than previously thought. However, the reliance on specific theoretical frameworks, like boundary conformal field theory, introduces inherent limitations. While these tools provide valuable insights, their accuracy depends on the validity of their underlying assumptions. Future research must focus on validating these theoretical predictions with direct experimental observations and exploring the behaviour of the system under more extreme conditions. Moreover, extending this approach to incorporate interactions between multiple impurities represents a crucial next step, potentially revealing entirely new collective phenomena and pushing the boundaries of our understanding of quantum materials. 👉 More information 🗞 Interplay between non-Fermi liquid and non-Hermiticity: A multi-method study of non-Hermitian multichannel Kondo model 🧠 ArXiv: https://arxiv.org/abs/2602.13749 Tags: