Magnetic-Field-Enhanced Incommensurate Magnetic Order in the Underdoped High-Temperature Superconductor ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathbf{O}}_{6.45}$

We present a neutron-scattering study of the static and dynamic spin correlations in the underdoped high-temperature superconductor ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{6.45}$ in magnetic fields up to 15 T. The field strongly enhances static incommensurate magnetic order at low temperatures and induces a spectral-weight shift in the magnetic-excitation spectrum. A reconstruction of the Fermi surface driven by the field-enhanced magnetic superstructure may thus be responsible for the unusual Fermi surface topology revealed by recent quantum-oscillation experiments.

Figure 1

(a)–(c) Elastic scans along $Q_H$ at fixed $Q_K=0.5$ and $Q_L=1$. The lines are results of two-Gaussian fits to the data. Panels (a) and (b) compare the incommensurate spin modulation at $H=0$ and at $H=14.9\mathrm{T}$ at low temperatures ($T=2\mathrm{K}$). The background at $T=50\mathrm{K}$ was subtracted. Panel (c) visualizes the effect of applying $H=14.9\mathrm{T}$ at $T=2\mathrm{K}$ by subtracting the intensity at $H=0$ from the intensity at $H=14.9\mathrm{T}$. (d) Raw (uncorrected) rocking scan profile at $H=14.9\mathrm{T}$ through the incommensurate peak at $(0.56,0.5,1)$ along the reciprocal-space trajectory indicated in the inset. Closed circles indicate the intensity at 2 K and open circles the intensity at 50 K.

Figure 2

Dependence of the elastic peak intensity at the incommensurate position $(0.56,0.5,1)$ on the external field at $T=2\mathrm{K}$. The data were extracted from the scans shown in Fig. 1 and scans similar to those. The line is the result of a linear fit to the data points.

Figure 3

(a) Inelastic scans at $E=3\mathrm{meV}$ and $T=2\mathrm{K}$ along $Q_H$ at fixed $Q_K=0.5$ and $Q_L=1$. Black squares indicate the raw scattering intensity at $H=0$ and open circles the intensity at $H=14.9\mathrm{T}$. The lines represent the results of two-Gaussian fits to the data. (b) Energy dependence of the magnetic peak intensity at the incommensurate position $(0.56,0.5,1)$ in zero field (closed squares) and in $H=13.5\mathrm{T}$ (open circles), corrected for the background. Note the logarithmic intensity scale.