SCIENCE sciencemag.orgPHOTO: EMILIO SEGRE VISUAL ARCHIVES/AMERICAN INSTITUTE OF PHYSICS/SCIENCE SOURCE
By Patrick A. Lee^1 and N. Phuan Ong^2P
hilip Anderson, groundbreaking
physicist, died on 29 March at the
age of 96. During his prolific career,
Anderson launched many major
branches of condensed matter phys-
ics. He excelled in extracting deep,
foundational principles from raw experi-
mental data and designed models that el-
egantly captured the essence of seemingly
intractable quantum phenomena.
Anderson was born on 13 December 1923
in Indianapolis, Indiana. After obtaining his
Ph.D. in physics from Harvard University in
1949 under the guidance of John H. Van
Vleck, Anderson joined Bell Labs (where
P.A.L. met him). In 1975, he joined the fac-
ulty at Princeton University (where he met
N.P.O.) and remained there until his retire-
ment in 1996.
Anderson had an uncanny ability to sniff
out the deep questions raised by experi-
mental data. In the late 1950s, experiments
on silicon had found that the diffusion of a
spin wave packet became anomalously slow
at a temperature of 4 K. Anderson theo-
rized that this “localization” (which he ini-
tially called “cisport,” a wordplay on “trans-
port”) resulted from coherent interference
of multiple reflections of the wave packet
in a disordered crystalline environment.
This 1958 prediction, dubbed “Anderson
localization,” was cited in his 1977 Nobel
Prize. In the 1980s, Anderson localization
blossomed into a major experimental in-
dustry, and it has since been applied to op-
tics, astronomy, ultracold atoms, and tumor
detection in mammography.
Anderson’s work in the 1950s also laid the
foundation for the modern theory of mag-
netism by explaining how electron spins
form local magnetic moments. This is an ex-
ample of broken symmetry, where a system
has less symmetry than suggested by basic
physical laws. In a 1972 article in Science ti-
tled “More is different,” Anderson expanded
on this concept, emphasizing that knowing
the laws of physics at the microscopic level
is not sufficient for understanding nature
on a macroscopic scale. Anderson resolved
another fundamental problem soon afterphysicists John Bardeen, Leon Cooper, and
John Robert Schrieffer published the theory
of superconductivity in 1957. The symmetry
breaking that was identified was expected
to lead to a zero-mass mode, which was
not seen in a superconductor. Anderson
resolved this puzzle by pointing out that,
in a superconductor, the wave function is
coupled to the electromagnetic field, which
merges with the zero-mass mode to become
the familiar plasma oscillations. The pho-
ton has acquired a mass inside the super-
conductor. Anderson recognized that this
mechanism solved the important problem
of unwanted massless particles in theories
hotly pursued at the time to unify quantumelectrodynamics and weak interactions.
Physicist Peter Higgs and others carried out
the fully relativistic formulation, but Higgs
gave Anderson credit in his paper and
Nobel lecture. The Anderson-Higgs mecha-
nism is now a cornerstone of particle and
condensed matter physics.
Shortly after the discovery in 1986 of
high-temperature (high-Tc) superconduc-
tivity in cuprates, Anderson proposed a
radical theory. He suggested that the par-
ent state of the high-Tc superconductor
is a magnetic insulator driven by strong
electron repulsion. Removing some of
the electrons by chemical substitution al-
lows the vacancies (“holes”) to move freely
and conduct current. Anderson’s identi-
fication of the parent state is now univer-sally accepted. To explain why the mobile
holes pair up to realize superconductiv-
ity, Anderson invoked the physics of spin
liquids, which he pioneered in 1973. In a
spin liquid, spins fail to attain the antifer-
romagnetic state because of conflicting lat-
tice constraints and quantum fluctuations.
Anderson called this the resonating valence
bond (RVB) state. He proposed that when
carriers are introduced into this state, it be-
comes a superconductor. These revolution-
ary ideas encountered considerable resis-
tance. Today, although Anderson’s specific
mechanism remains controversial, many of
the ideas in his 1987 paper, such as super-
conductivity arising from strong repulsion,
have gained wide acceptance. The RVB
state is the archetypal example of a quan-
tum spin liquid, currently a topic of intense
interest. Another idea of great importance
is that the excitations of the spin liquid be-
have as electrons that have lost their charge
but retain their spin. This early example of
the notion of fractionalization is supported
by exactly soluble models as well as by re-
cent experiments. In time, Anderson’s spin
liquid RVB theory may well be remembered
as his most profound and prescient.
Despite being a self-professed curmud-
geon, Anderson was compassionate and
amazingly loyal to friends and colleagues.
Former students who had hit a rough patch
often moved back to Princeton to work with
him until they regained their footing. After
learning that a collaborator had suffered a
stroke, Anderson flew to stay with him for
a week. He had a puckish sense of humor.
During dinners that he and his wife, Joyce,
regularly hosted, Anderson, offering coffee,
would ask each guest “caffeine or non?”
He would then prepare a single pot mixed
with the correct proportions of each. To our
amusement, he and Joyce took great plea-
sure in belting out songs by Tom Lehrer
(a friend from college). Both held strong
antiestablishment convictions. At the height
of the Vietnam War, Anderson was once
detained by security for posting “Stop the
Bombing” pamphlets at Bell Labs. He was
a vocal opponent of the Strategic Defense
Initiative. Well into his 90s, Anderson re-
tained a vibrant curiosity. He wanted to
know who Dr. Dre was (a frequent clue in
the New York Times crossword puzzle) and
wanted to hear “Desolation Row” after Bob
Dylan’s Nobel Prize win.
Anderson’s expansive intellect, his pas-
sion, and the special insights he brought to
everything he touched will be sorely missed.
His passing marks the loss of the last of the
intellectual giants who shaped the field of
quantum matter. j10.1126/science.abc1042RETROSPECTIVEPhilip W. Anderson (1923–2020)
Intellectual giant of condensed matter physics
(^1) Department of Physics, Massachusetts Institute of
Technology, Cambridge, MA, USA.^2 Department
of Physics, Princeton University, Princeton, NJ, USA.
Email: [email protected]; [email protected]
1 MAY 2020 • VOL 368 ISSUE 6490 475