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arXiv:0704.0888 · Physical Review B

Nuclear magnetic resonance evidence for a strong modulation of the Bose-Einstein condensate in BaCuSi 2 O 6

S. Krämer, Raivo Stern, M. Horvatić, C. Berthier, T. Kimura, I. R. Fisher

Published Sep 18, 2007• 33 citations
arXivHTMLPDF

Abstract

We present a $^{63,65}\mathrm{Cu}$ and $^{29}\mathrm{Si}$ NMR study of the quasi-2D coupled spin 1/2 dimer compound ${\mathrm{BaCuSi}}_{2}{\mathrm{O}}_{6}$ in the magnetic field range $13--26\phantom{\rule{0.3em}{0ex}}\mathrm{T}$ and at temperatures as low as $50\phantom{\rule{0.3em}{0ex}}\mathrm{mK}$. NMR data in the gapped phase reveal that below $90\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ different intradimer exchange couplings and different gaps $({\ensuremath{\Delta}}_{\mathrm{B}}∕{\ensuremath{\Delta}}_{\mathrm{A}}=1.16)$ exist in every second plane along the $c$ axis, in addition to a planar incommensurate (IC) modulation. $^{29}\mathrm{Si}$ spectra in the field induced magnetic ordered phase reveal that close to the quantum critical point at ${H}_{\mathrm{c}1}=23.35\phantom{\rule{0.3em}{0ex}}\mathrm{T}$ the average boson density $\overline{n}$ of the Bose-Einstein condensate is strongly modulated along the $c$ axis with a density ratio for every second plane ${\overline{n}}_{\mathrm{A}}∕{\overline{n}}_{\mathrm{B}}\ensuremath{\simeq}5$. An IC modulation of the local density is also present in each plane.

DOI
10.1103/physrevb.76.100406

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