Observation of gapless collective charge fluctuations in an Anderson insulating state
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arXiv
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| Main Authors: | , , , , , , , |
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| Format: | Preprint |
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2025
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| _version_ | 1866914274212839424 |
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| author | Ok, Jong Mok Park, Beom Jun Hwang, Junik Park, Seonghoon Kang, Myeongjun Kim, Jun Sung Kim, Ki-Seok Baek, Seung-Ho |
| author_facet | Ok, Jong Mok Park, Beom Jun Hwang, Junik Park, Seonghoon Kang, Myeongjun Kim, Jun Sung Kim, Ki-Seok Baek, Seung-Ho |
| contents | Understanding the nature of collective charge dynamics in the Coulomb gap phase is essential for revealing the existence of many-body localization. However, the corresponding many-particle excitation spectra remain poorly understood. Here, we present a comprehensive investigation of $^{27}$Al and $^{63}$Cu nuclear magnetic/quadrupole resonance (NMR/NQR), along with specific heat ($C_p$) measurements, in the $p$-type semiconductor CuAlO$_2$. Our study unveils distinct changes in charge dynamics at two crossover temperature scales which separate three regimes associated with Anderson localization of charge carriers: thermally activated transport ($T>150$ K) $\rightarrow$ Mott variable-range hopping (VRH) $\rightarrow$ Efros-Shklovskii (ES) VRH with Coulomb gap formation ($T<50$ K). In the ES VRH regime, we observe a striking divergence in the zero-field $^{63}$Cu spin-lattice relaxation rate, $(T_1T)^{-1}$, which is strongly suppressed by an applied magnetic field, indicative of quantum critical charge fluctuations. This is further supported by a distinct magnetic field-dependence of $C_p/T$ deep within the Coulomb gap phase. Taken together, these results provide compelling evidence for the emergence of strong, gapless collective charge fluctuations within the Anderson insulating phase where single-particle excitations are gapped. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2508_07215 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Observation of gapless collective charge fluctuations in an Anderson insulating state Ok, Jong Mok Park, Beom Jun Hwang, Junik Park, Seonghoon Kang, Myeongjun Kim, Jun Sung Kim, Ki-Seok Baek, Seung-Ho Strongly Correlated Electrons Understanding the nature of collective charge dynamics in the Coulomb gap phase is essential for revealing the existence of many-body localization. However, the corresponding many-particle excitation spectra remain poorly understood. Here, we present a comprehensive investigation of $^{27}$Al and $^{63}$Cu nuclear magnetic/quadrupole resonance (NMR/NQR), along with specific heat ($C_p$) measurements, in the $p$-type semiconductor CuAlO$_2$. Our study unveils distinct changes in charge dynamics at two crossover temperature scales which separate three regimes associated with Anderson localization of charge carriers: thermally activated transport ($T>150$ K) $\rightarrow$ Mott variable-range hopping (VRH) $\rightarrow$ Efros-Shklovskii (ES) VRH with Coulomb gap formation ($T<50$ K). In the ES VRH regime, we observe a striking divergence in the zero-field $^{63}$Cu spin-lattice relaxation rate, $(T_1T)^{-1}$, which is strongly suppressed by an applied magnetic field, indicative of quantum critical charge fluctuations. This is further supported by a distinct magnetic field-dependence of $C_p/T$ deep within the Coulomb gap phase. Taken together, these results provide compelling evidence for the emergence of strong, gapless collective charge fluctuations within the Anderson insulating phase where single-particle excitations are gapped. |
| title | Observation of gapless collective charge fluctuations in an Anderson insulating state |
| topic | Strongly Correlated Electrons |
| url | https://arxiv.org/abs/2508.07215 |