Magnetization in the ultraquantum limit.

The prediction of magnetic field induced diamagnetism in metals, with a quantized oscillatory behavior, was first made by Landau in 1930 [1], and within the same year the discovery of magnetic quantum oscillations in bismuth by de Haas and van Alphen [2] was made. Since that time there have been numerous searches for the magnetic behavior of materials above the n 1 Landau level (quantum limit) [3]. Many of these searches have been made on semimetallic Bi because it is known to have one of the smallest volume Fermi surfaces (FS), and therefore small quantum limit values of magnetic field, of any known pure material. However, these searches and their interpretations have been hindered because the low carrier concentration is magnetic field dependent making the analysis of the experimental results difficult. In this Letter we report measurements on LaRhIn5 [4], a high electrical conductivity normal metal, in which we are able to observe quantum oscillations below the quantum limit from a piece of FS that occupies an extremely small part of the overall FS volume. The contribution to the overall sample magnetization due to the electrons in this FS pocket at fields far above the quantum limit (ultraquantum limit) has been measured and the results compared to a theoretical model that describes the measured data extremely well. In the presence of a magnetic field, Onsager [5] showed that the orbital motion of electrons in metals is restricted to lie on tubes in k (wave vector) space, Landau tubes, determined by the condition of area quantization: AE, kB n 1 1 2peB