Commensurate antiferromagnetic excitations as a signature of the pseudogap in the tetragonal high-Tc cuprate HgBa2CuO4+δ

Abstract

Antiferromagnetic correlations have been argued to be the cause of the d-wave superconductivity and the pseudogap phenomena exhibited by the cuprates. Although the antiferromagnetic response in the pseudogap state has been reported for a number of compounds, there exists no information for structurally simple HgBa2CuO4+δ. Here we report neutron-scattering results for HgBa2CuO4+δ (superconducting transition temperature Tc≈71 K, pseudogap temperature T*≈305 K) that demonstrate the absence of the two most prominent features of the magnetic excitation spectrum of the cuprates: the X-shaped ‘hourglass' response and the resonance mode in the superconducting state. Instead, the response is Y-shaped, gapped and significantly enhanced below T*, and hence a prominent signature of the pseudogap state.

Model for the neutron resonance in HgBa2CuO4+δ

“…Moreover, a precursor of this resonance exists in the PG above T c , the SC critical temperature 21 where the resonance is observed at the same frequency ω res than in the SC state with a lower intensity. The latter has also been observed in other cuprate compounds [12][13][14][15][22][23][24] .…”

“…This feature has been observed in other cuprate compounds [24][25][26][27][28] . 3) A very specific doping dependence of the spin fluctuations is reported in monolayer Hg-based cuprate compound Hg-1201 21 . In the underdoped regime, at hole doping below 0.12 (p < 0.12), a Y-shape has been observed close to the vector Q in both the PG and the SC phase without any change at T c .…”

“…It has first been observed by INS experiments around the AF wave vector Q= (π, π) at a frequency ω res = 41 meV in YBa 2 Cu 3 O 7−δ (YBCO) [4][5][6][7][8][9][10][11][12][13][14][15] and at similar energies in other compounds [16][17][18][19][20] in the superconducting (SC) phase. In this paper, we focus our study on recent experiments performed in monolayer Hgbased cuprate compounds: HgBa 2 CuO 4+δ (Hg-1201) 21 . This compound represents a perfect playground to study the physics of cuprates superconductors.…”

“…1) The resonance stands below the 2∆ 0 SC threshold of particle-hole continuum (∆ 0 SC is the maximum of the dwave superconducting (SC) gap) and the frequency resonance ω res decreases with underdoping 21 . Moreover, a precursor of this resonance exists in the PG above T c , the SC critical temperature 21 where the resonance is observed at the same frequency ω res than in the SC state with a lower intensity.…”

“…2) The energy fluctuation spectrum around Q has a peculiar behavior and distribution in phase space in the underdoped regime 21 . The low and high energy parts of the fluctuation spectrum behave differently with temperature.…”