Abstract
The first indication of a pseudogap in cuprates came from a sudden decrease of NMR Knight shift at a doping-dependent temperature $T^*(\delta)$. Since then, experiments have found phase transitions at a lower $T^*_\text{phase}(\delta)$. Using plaquette cellular dynamical mean-field for the square-lattice Hubbard model at high temperature, where the results are reliable, we show that $T^*(\delta)$ shares many features of $T^*_\text{phase}(\delta)$. The remarkable agreement with several experiments, including quantum critical behavior of the electronic specific heat, supports the view that the pseudogap is controlled by a finite-doping extension of the Mott transition. We propose further experimental tests.
Highlights
A doping-dependent temperature T ∗, early studies of cuprate high-temperature superconductors found a decrease in the NMR Knight shift [1,2,3,4,5]
Polarized neutron diffraction [6,7,8], Nernst effect measurements [9], ultrasound measurements [10], terahertz polarimetry [11], and optical anisotropy measurements [12] report that the prototypical YBa2Cu3Oy undergoes a thermodynamic phase transition that breaks time-reversal, spatial inversion, twofold rotational, fourfold rotational, and mirror symmetries below tahdaonpTin∗g-adtelpoewnddeonpt itnegm. pTehraistusruegTgp∗ehasstes that is distinctly lower that phase transitions are a consequence of the pseudogap first observed in NMR, not the cause [13,14]
The remarkable agreement that we find with several experiments supports the view that the high-temperature physics of the pseudogap is controlled by a finite-doping extension of the Mott transition that includes superexchange effects [16]
Summary
A doping-dependent temperature T ∗, early studies of cuprate high-temperature superconductors found a decrease in the NMR Knight shift [1,2,3,4,5]. Recent Hall measurements on YBa2Cu3Oy (YBCO), La2−xSrxCuO4 (LSCO), and La1.6−xNd0.4SrxCuO4 (Nd-LSCO) highlighted a sharp jump in carrier density with increasing hole doping δ across a material-dependent critical doping δp∗hase at which the Tp∗hase line suddenly drops [18,19,20] This drop, observed in Raman scattering experiments on Bi2Sr2CaCu2O8+δ (Bi2212) [21], occurs between a lowdoping antiferromagnetic Mott insulating regime [22] and a high-doping metallic regime [23]. Even if the low-temperature normal-state phase diagram is usually metastable, hidden by more ordered states, the associated high-temperature crossover regime can be observed in a doped organic compound owing to magnetic frustration [88] In both doped Mott insulators [14,86,89] and doped charge-transfer insulators [90], the Knight shift pseudogap T ∗ line is parallel to the Widom line and appears as a high-temperature precursor of this crossover line. These CDMFT studies retrieve the aforementioned maximum in entropy close to δ∗ [85] and a van Hove-like singularity at higher doping [14]
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