Symmetry-determined generalized ferromagnetism in multi-valley electron fluids
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| Format: | Preprint |
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2025
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| _version_ | 1866915376436084736 |
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| author | Calvera, Vladimir Berg, Erez Kivelson, Steven A. |
| author_facet | Calvera, Vladimir Berg, Erez Kivelson, Steven A. |
| contents | Quantum electronic fluids with spin and valley degrees of freedom have a correlation driven tendency to flavor polarization (generalized ferromagnetism). To first order in the long-range Coulomb interactions -- i.e. in the Hartree-Fock approximation -- spin and valley polarization exhibit a spurious degeneracy. We show that to second order -- or more generally in the random-phase approximation -- this degeneracy is lifted in a way that depends only on the underlying symmetry relating the two valleys. In two spatial dimensions, if the valleys are related by an $n-$fold rotation ($n>2$) or by mirror reflection and each valley is invariant under $C_2$ or time reversal (as is the case in AlAs quantum wells) then valley polarization is preferred. If the valleys are related by time reversal or by $C_2$ rotation symmetry (as in multilayer graphene systems) then spin order is selected. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2507_05344 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Symmetry-determined generalized ferromagnetism in multi-valley electron fluids Calvera, Vladimir Berg, Erez Kivelson, Steven A. Strongly Correlated Electrons Mesoscale and Nanoscale Physics Quantum electronic fluids with spin and valley degrees of freedom have a correlation driven tendency to flavor polarization (generalized ferromagnetism). To first order in the long-range Coulomb interactions -- i.e. in the Hartree-Fock approximation -- spin and valley polarization exhibit a spurious degeneracy. We show that to second order -- or more generally in the random-phase approximation -- this degeneracy is lifted in a way that depends only on the underlying symmetry relating the two valleys. In two spatial dimensions, if the valleys are related by an $n-$fold rotation ($n>2$) or by mirror reflection and each valley is invariant under $C_2$ or time reversal (as is the case in AlAs quantum wells) then valley polarization is preferred. If the valleys are related by time reversal or by $C_2$ rotation symmetry (as in multilayer graphene systems) then spin order is selected. |
| title | Symmetry-determined generalized ferromagnetism in multi-valley electron fluids |
| topic | Strongly Correlated Electrons Mesoscale and Nanoscale Physics |
| url | https://arxiv.org/abs/2507.05344 |