<i>T_c</i> and Other Cuprate Properties in Relation to Planar Charges as Measured by NMR

• Main Authors: Michael Jurkutat, Andreas Erb, Jürgen Haase
• Format: Article
• Language: English
• Published: MDPI AG 2019-07-01
• Series: Condensed Matter
• Subjects: NMR; cuprates; charge order
• Online Access: https://www.mdpi.com/2410-3896/4/3/67

Nuclear magnetic resonance (NMR) in cuprate research is a prominent bulk local probe of magnetic properties. NMR also, as was shown over the last years, actually provides a quantitative measure of local charges in the CuO<inline-formula><math display="inline"> <semantics> <msub> <mrow></mrow> <mn>2</mn> </msub> </semantics> </math> </inline-formula> plane. This has led to fundamental insights, e.g., that the maximum <inline-formula> <math display="inline"> <semantics> <msub> <mi>T</mi> <mi>c</mi> </msub> </semantics> </math> </inline-formula> is determined by the sharing of the parent planar hole between Cu and O. Using bonding orbital hole contents on planar Cu and O measured by NMR, instead of the total doping <i>x</i>, the thus defined two-dimensional cuprate phase diagram reveals significant differences between the various cuprate materials. Even more importantly, the reflected differences in material chemistry appear to set a number of electronic properties as we discuss here, for undoped, underdoped and optimally doped cuprates. These relations should advise attempts at a theoretical understanding of cuprate physics as well as inspire material chemists towards new high-<inline-formula><math display="inline"> <semantics> <msub> <mi>T</mi> <mi>c</mi> </msub> </semantics> </math> </inline-formula> materials. Probing planar charges, NMR is also sensitive to charge variations or ordering phenomena in the CuO<inline-formula><math display="inline"> <semantics> <msub> <mrow></mrow> <mn>2</mn> </msub> </semantics> </math> </inline-formula> plane. Thereby, local charge order on planar O in optimally doped YBCO could recently be proven. Charge density variations seen by NMR in both planar bonding orbitals with amplitudes between 1% to 5% appear to be omnipresent in the doped CuO<inline-formula><math display="inline"> <semantics> <msub> <mrow></mrow> <mn>2</mn> </msub> </semantics> </math> </inline-formula> plane, i.e., not limited to underdoped cuprates and low temperatures.